This page is dedicated to the Teachers and Education Administrators who make the sacrifices and meet the challenges, often without recognition, daily to educate our youth.
"It is the supreme art of the teacher to awaken joy in creative expression and knowledge." - Albert Einstein
This page is an presentation of RadioShack's Network 3, an early networking implementation for the TRS-80 using the RS232 protocol to share resources and programs with multiple computers. The system and software are designed to aid Teachers and Students in the Classroom using the TRS-80 Microcomputer and its educational programs.
The system comprises a single host with a hard disk, printer, 1 or 2 floppy drives, and the Network 3 Controller. The Network 3 Controller enables users to operate up to 16 TRS-80 Model 4 or III Microcomputers as Student Stations in a classroom network. They are connected using serial cards (RS232) to the Network 3 Controller. The hard disk is connected to the system bus and the network controller to the host serial port. Once configured and installed, the Network 3 Host software emulates TRSDOS 1.3 and allows other machines to share the resources connected to the host. (All Model 4 computers in the Network 3 system operate in the Model III mode.) The software works with the controller to poll the individual ports and automatically listen for calls from student stations.
The Network system provides the student stations with most of the capabilities of a stand-alone, disk-equipped Model III system with a hard drive. Student Stations load and store BASIC and system programs using the hard disk attached to the host, which was much faster and provided more room than the floppy-only version. The host software also includes a spooler when a printer is connected to the host. Students can print and move on to other tasks without interrupting other students or the teacher.
To summarize, this system allowed schools and teachers to utilize the TRS-80 and educational software with large classrooms of students. It is an early implementation of a file and printer sharing platform using RS232 and software written to work together. Below is a diagram of a fully utilized Network 3 system with a supporting Network 2 appliance.
This page will cover the hardware, including the Model III and 4 microcomputers, the hard drive, and the Network 3 and Network 2 appliances. We'll cover the steps used to recover the software, how the software works and is installed, and how the system is connected to function. There is a gallery at the end with photos from the July 2022 DFW Retro Computers - Show and tell, browse, discuss vintage computers event, showing the working system on display.
Here is an entire two-page layout of the educational software titles hosted at RadioShackCatalogs.com. Math, physics, typing, and reading academic titles are on the left. K-8 Math with Student Management shipped with extra software that runs on the Network 3 and automatically tallies scores and grades for teachers.
The three BASIC Programming instructional courses are on the right, a complete instruction set with 25 student workbooks. These courseware titles have over 150+ transparencies and complete lessons to teach the BASIC programming language. Unfortunately, some of the more complicated titles required either the TRS-80 Pilot Plus or AUTHOR I authoring systems, neither of which have been recovered to our knowledge.
A few titles have been located, including the initial model 1 K-8 Math, which we have loaded into the system. These are math lessons written in BASIC for grades K-8. There were many titles for this system we hope to recover in the future.
Above is the overview and layout of a fully complemented Network 3 Setup with the supporting Network 2 appliance.
First, let's talk about the computers; the Model III is a Z80-based 8-bit Microcomputer with 16-48K memory. The system runs at 2MHz, supports a 16x64 character display, and can be upgraded with a hi-resolution (512x192) display add-on option. Full-featured models included a double-density diskette drive controller and single-sided diskettes.
According to surveys conducted by RadioShack, Schools from several states were polled and responded between 1980 and 1982. According to RadioShack contracts, Pennsylvania spent nearly a million dollars on TRS-80s in 1981. Reports from the Department of Education of Florida and Oklahoma used 50 and 70% TRS-80s by 1982, respectively. The Model III was a worthy competitor to the other classroom setups of the day.
The Model IIIs used in schools were primarily diskless to save costs, making loading programs only from cassette or coding at the console possible. Students usually loaded BASIC or machine language programs from a cassette player or typed them in at the console. To turn in information for review or grading, students must save work to tape for transport to the teacher's station for printing and assessment.
Adding the RS232 option card to existing model IIIs and joining them to a Network 3 setup significantly increased the functionality of student stations and decreased the time spent by Teachers addressing tape issues and reviewing and grading work. The students gained access to an emulated TRSDOS 1.3 Disk System environment, with an additional hard disk and shared printer. Students could also access Network BASIC, which is Model III BASIC with a few additional Network 3 specific commands.
The TRS-80 Model 4 and 4D were the last of the line for the Z80-based desktops of this scale. The Model 4 retained backward compatibility of the Model III and added a dedicated soundboard, up to 128k memory, a 4MHz CPU, and new Operating System options like CP/M, TRSDOS, and LS-DOS. The display also featured an 80x24 B&W (Later Green) CRT and, like the predecessor, a high-resolution bitmap graphics option (640x240).
Tandy RadioShack planned and added supporting logic and a socket for the Z800 16bit CPU. Still in development with Zilog at the time of the Model 4 release, the CPU promised backward compatibility with the Z80 instruction set, faster speeds, and the ability to break the 128K memory barrier. After multiple missed delivery dates, Tandy Engineers removed the Z800 socket and supporting logic from the later Model 4P and Gate Array 4s.
Tandy shipped the Model 4D with newer features, 2 Double-Sided TEC floppy drives, an updated keyboard (to match growing standards), an updated, sharper CRT, and Deskmate, as indicated by the D signification. The upgrades resulted in a much easier-to-view display, more storage space, and a new productivity suite.
What is Gate Array? Gate Array Logic (GAL) chips are custom fabricated and programmed for specific functions. They contained enough transistors to reduce the number of supporting gates and other logic on the main logic board. This enhancement allowed Tandy to consolidate the FDC and RS232 options onto the main logic board, making it a single-board computer (SBC) and reducing costs.
During the first years of production, the main logic board used programmable array logic (PAL). The larger chipset resulted in a larger plane of supporting logic gates and other chips. The floppy disk controller and RS232 serial option cards were separate boards mounted behind the main logic board. The 4D reduced the costs and footprint of the main logic and improved the overall speeds with true 0-wait states, reflecting the full 4MHz CPU speed.
The software for the Network 3 came up for auction online, listed with the binder and two diskettes. This listing was the event that spawned this entire process resulting in the exhibit. Storage Unit Buyers recovered the software from a Florida unit from a previous RadioShack owner who passed away, as the seller informed us. The diskettes were molded but not creased or damaged, thankfully. The binder appeared in good shape, with all pages.
Not realizing what we purchased, after arrival and review, we discovered this had a different catalog number, 26-2778. This software package is the Hard Disk specific version that further expands the use of the Network 3 using a hard drive. The Network 3 Operating System (Cat. No. 26-2775) was designed to run from floppy drives, limiting the use and space for student files and programs.
Since this software had not yet been archived, it was time to get them imaged and see if we could recover the install set. The package came with two diskettes; the Network 3 Operating System for Model III Hard Disk with LDOS and the Network 3 Student Software. Both diskettes are single-sided, double-density 180K media.
Each "cookie" (the internal diskette media) needed to be removed from its original jacket and cleaned with light soapy water. Afterward, due to concerns about the plastics absorbing water, we allowed the media to air dry for 24hrs. After placing the media in new jackets, we used Dave Dunfield's ImageDisk 1.18 to grab the images using the AST 486 disk station.
The first attempt to read the diskette was not met with success. Our imaging station uses NOS TEAC DSDD 5.25" floppy drive, running under DOS 5.02. As seen in the read errors from ImageDisk, the floppy media was still too dirty. After more cleaning, another 24hr drying period, and a drive cleaning, we successfully recovered both diskette images with 0 errors.
Using the IMDs (ImageDisk Files) and converted HxC floppy images (HxC2001 Floppy Emulator), we passed them up to experienced and talented TRS-80 enthusiasts and experts for feedback. Several reported the diskette images looked good and were booting and reading in emulated systems.
Now it was time to review the contents to see what software exists. Note there are hidden files not shown here, like NBASIC and other system files; these were the files that appeared on the first directory read. We reviewed the documentation and provided a summary of each file:
The second diskette in the set is the student software, which uses TRSDOS to start the system and automatically launch the disk-based student software. Four files are present:
When we recovered the software, we did not yet have the Network 3 controller or a hard drive; we can still test the host application and see if it runs; it seems to run without having the Network 3 connected. Starting up HOST/CMD, the console asks for the maximum baud rate for the network (9600 baud) and loads up the status screen. The status screen shows the name of the software running and its version. Below are the status lines that reflect the activity of the host. As each student station makes requests, the currently serviced student station number is shown according to the connected port. The spool line indicates any students spooling files to the printer, and files indicate the number of open files on the host.
We can see that the software is copyrighted Micro-Systems Software, Inc., 1982. The data indicates the software was licensed to Tandy Corporation by Micro-Systems Software Inc. Micro-Systems Software was also behind the creation of DOSPLUS, a popular alternative operating system for the TRS-80 line of computers. Micro-Systems Software Inc. wrote more titles on other computer architectures as the company progressed throughout the 1980s.
The first diskette with the host support files above is an LDOS data diskette, requiring a booting LDOS system to view the contents. The student diskette, however, is bootable and uses TRSDOS 1.3 to load the DSTUDENT program automatically. This program automatically loads the student software from floppy, bringing the student to the Network 3 prompt. No commands will work until the systems are all connected, as indicated by the missing flashing prompt.
The Student Diskette also contains the first part of a conversion program used to install software from TRSDOS and possibly other foreign diskette formats. A copy of this diskette is used to modify and transfer programs to run on the Network 3. The software manual includes more information on what software requires conversion and what titles had unique Network 3 releases.
The story almost ended here, with just a pretty binder and recovered diskette images. We were surprised to find out a collector was willing to sell a real Network 3, the other half of this hardware/software combo! The Network 3 appliance had not been tested and appeared to be missing the power switch light cover; we would need to source a power supply since those items are not usually found alone. That was not enough to stop us from jumping on the opportunity to add this unique TRS-80 item to the collection.
Luckily it is the same power supply brick used with the TRS-80 and Expansion Interface, and we already had a couple to at least test the appliance. A few weeks later, we located a pair of power supplies from another collector. The last piece was to replace the colored cover for the power switch. We sourced an extra button from a parts model with a similar switch type; as indicated in the catalogs, we used a red cap to complete the setup.
The Network 3 Controller connects the host and sixteen student stations via an RS-232C Interface using DB-25 connectors mounted on the rear panel for each student station and the host. These connectors are designed for standard cables with male connectors. The controller functions under two modes, the main difference being the source of the polling clock. Depending on which mode is selected, the clock can be derived from the host or an internal 555 timer.
A two-position switch on the front panel can select either of two modes: Polling or Auto Select. The button has a small light to indicate when in auto mode. The Network 3 Controller, at a command from the host, selects the first logical client (one of sixteen computers) and forms a full duplex serial data path between the host and the selected computer. A Request To Send (RTS) is routed from that client to the host and is used by the host to determine if the client is requesting service. The Host operator selects the next logical client and tests the service request status if no service is requested.
If a selected client requests a service, the host sends an ENO character (Enter Question) to the client, and the client must reply with a series of characters that define the service requested (i.e., LOAD, SAVE, RPRINT). The host then services the request, and the Host operator selects the next logical client. This process continues until all sixteen clients have been polled. The Host operator selects the first logical client, station 1, and begins the polling process again.
The second mode of operation, Auto Mode, allows the Network 3 Controller to test the service request signal of each client in turn and will stop on any channel that has an active service request. An acknowledge signal is sent to the selected client, indicating that the client may send a sequence of characters that define the service requested. When the selected client has been serviced, it must release the service
request signal. The release allows the Network 3 Controller to resume searching for an active request from other channels.
The Network 2 Microcomputer was the predecessor to the Network 3 but worked differently. The Network 2 Microcomputer used the cassette ports of the host and student stations to transfer programs and data. The Network 2 had limited bandwidth, maxing out at 1500 for Model III or 500 baud for Model 1 systems. The appliance operates in two modes, Multiplex and Cassette. Multiplex allows the host to send data to all 16 students simultaneously, sourced from the CPU. Cassette mode reverses the direction enabling the teacher to dial in a single student station for returning data, i.e., programs usually coded in BASIC.
While saving time loading software to student stations, the system did not support request management. In fact, the computers did not require any specific software; the CSAVE and CLOAD commands were used as if loading or sending to a tape recorder. When the Network 3 was released, the design incorporated the Network 2 to load the student software and played a functional role in saving time. A NET2/JCL script loads the student software into memory and pipes it out the cassette port to get diskless systems on the network. The Network 2 plays a viable role and remains a functional part of the Network 3 exhibit.
With a real Network 3 in hand, seven possible systems to use as students or hosts, and now the software recovered, it was time to tackle the last part of the setup. The TRS-80 Hard Disk Systems are in a league of their own regarding getting them working. Without the documented and recovered history covering the alteration and how these drives work, enthusiasts like us would lose this information and the practical use of these drive systems.
We are very thankful for the hard work from the TRS-80 Community to preserve the valuable software for these systems.
The Tandy RadioShack hard disk systems are composed of 3 main parts:
The controller (HDC) (Tandy Part AX-9282) is an early Western Digital controller based on the Signetics 8x300 microcontroller. It's referred to as the Western Digital 1000 (WD1000) or the "8x300 board," depending on who you ask. The board operates at 8MHz, includes 16K (4116 DRAM) as cache, and supports connections for up to 4 different diskette bubbles supporting up to 8 heads and 1024 cylinders or tracks. The math yields roughly 68MB per hard disk bubble using upgraded drives. Additional hard disks were connected via ribbon cables routed out of the back of the drive system, located in identical secondary systems that did not have a controller, only a power supply and disk bubble.
Four or five generations of controller boards and corresponding host cards existed for the larger business systems. According to historical accounts from folks who worked at Tandy and other sources that worked on the project, the early type board seen here was very close to the prototype boards sent by Western Digital. The controller emulated the WD1010 future implementation using separate logic. Later, boards were reduced in size when Western Digital released the 1010 controllers, which integrated the function of several chips into just two, resulting in a board half the size.
The power supply was the first problem; it required service to remove known components expected to fail. As explained in previous pages, this power supply contains the "foil/paper sealed in oil" RIFA capacitors. These are the ones that usually release the mess of smoke due to age and design. After replacing them and checking for correct voltages, we proceeded to the Tandy Technical Service Bulletins for the hard disk controller.
Most, if not all, Tandy Computers have a list of technical bulletins used by Tandy Service Personnel to fix issues found after production and maintain customer equipment. We reviewed the list, and determined work was needed to bring the board back to working functionality. For example, while appearing to be correctly oriented, a set of series resistors placement is wrong; according to HD:10, the screen print was backward in drafting and not corrected before production. After correction, we reviewed and confirmed that RadioShack Service Personnel had likely completed all other technical bulletins.
Our initial testing showed the board did come to a ready state, as indicated by the activity light. Still, since we were making changes to the entire system, basic alignment checks were needed to ensure accurate read and write functionality. After the alignment checks were good, using the original hard disk bubble, it was time to modify the board to allow the use of almost any type and size of disk bubble.
RadioShack shipped this drive with the Tandon TM503. The disk bubble gets its designation 503 for having a 5 Mbps transfer rate and containing three platters with six heads. Three hundred six cylinders or tracks result in a maximum size of 15MB formatted.
After drive capacity increased over time, operators wanted to upgrade and take advantage of the size increase. The problem was TRS wanted consistent and desirable features for the hard disk systems, so they manually wired in write protection and drive select/activity lights.
Three wires from the controller board are tactically soldered to points on the MFM hard disk. While the system may run and detect another hard disk after removing the wires, operators will lose the ability to write to the disk and activity light functions. Further, the board is designed as a primary controller, the write protect signal (5vdc) and a signal that relayed power up to three external secondary disk systems (12vdc) were routed out the data cables to the secondary hard drive systems. The 12vdc signal would power up any auxiliary disk drives via a relay to the power supply. The operator would not have to remember and key on each drive system on startup physically.
TRS implemented write protection by sending 5v out the data cable on line 5 and tying that to the TP on the hard drive bubble. Using the lamp as a resistor, the switch, when pushed, would ground the line. The logic on the controller would detect this and send an interrupt to the operating system halting any writes to the disk. The Select Light and activity indication (blinking) was done using a NAND gate on the Disk Select and Seek Complete signals on the MFM bubble. If operators had more than one disk system, the light would illuminate when the drive was selected and flicker off during activity.
In an article written by Roy T. Beck, he describes a method for altering the setup that allows for retaining the features. It involves routing the signals (wires) back to the corresponding locations on the board and, if required, cutting the fifth and seventh lines out of the data cables. Checking the standards for the ST412/506 drives, signals on pins five and seven are not used; on the connectors of the emulator, they aren't routed to anything. After re-routing the signals according to the documents, it was time to use the MFM emulator to capture the actual disk image and use it in place.
David Gesswein designed a custom board that uses a Beaglebone SBC (Single Board Computer) to emulate the functions of an MFM hard drive. The unit is intended to read and replace failing MFM hard drives for archiving and to emulate one or two drives. The image created from the physical disk can be configured to run emulated by the device.
The board attached to the beagle bone has edge connectors connecting to the controller. The board also features a connector for a second data cable for emulating a second virtual hard disk. The board runs a customized image of Linux with software that handles the emulation and capture, under mostly an automated process. The software can effortlessly identify and analyze most MFM hard disks and read-in the data bit by bit, so long as the drive functions normally. We also use the option to include an extracted data file for analysis, which is convenient.
We successfully captured the image of the TM503 hard disk bubble we pulled from the 15MB Hard Disk System. Using the extracted data file, we found the image is a Xenix installation, which is interesting. We loaded the image into the trs80gp emulator and found the system boots to a Tandy 6000 Xenix disk image (A very popular Unix first written by Microsoft). We archived the disk image for later review, made a copy of the image, and proceeded with the hard disk format and setup for the Network 3 Operating Software.
To get started, we referenced Appendix IV and V of the Network 3 Operating Software manual, which covers initializing the hard disk and copying the software. The setup directions indicate we need the diskettes for the LDOS Hard Disk Operating System 5.1.4. The Network 3 software included a JCL script referred to earlier as EDUCINIT and started the process by running it first.
The Education Initialization is written to set up the system with six logical hard disks, using all combined MFM bubbles attached to the controller. With a single TM503 being emulated, this results in 15MB (6x2.5MB logical partitions). The EDUCINIT initialization file requires an installation password and copies specific configuration files to alter the standard LDOS 5.1.4 hard disk setup. The JCL file includes a line statement to patch the installation for "education use only."
The process uses a copy of LDOS 5.1.4 and formats the physical disk as six logical drives (0-3, 6, and 7) with 2.5MB each. Since the host contains two floppy drives, the system automatically configures them as drives 4 and 5 logically. The reason is to maintain compatibility with older software that expects hard disks to be drives 0-3 and floppy drives 4-7.
Once the drive is formatted, the software copies files from the LDOS Hard Disk setup to the first logical disk. In the last step setting up the drive, the system configuration, logical disk assignments, and other settings for starting the system are transferred to the initialization diskette for booting the system.
The process takes about an hour to complete using the actual hardware and around 25 minutes using the emulated hard drive. Once the formatting is complete, the operator is guided through finalizing the initialization floppy. This diskette is needed to start the host computer with the hard disk, as these systems were not designed to boot automatically. With these steps complete, the last step is to use the COPYTOHD JCL, which copies the Network 3 files to the hard disk.
We completed the installation successfully and set up the system with four student stations, a Model 3, Model 4, Model 4D, and Model 4P. We could load several games to the hard drive and share them between the student stations like a TRS-80 Arcade. Student stations can control the hard and floppy disk drives and even run Network BASIC. We moved all four devices across all four lanes of channels, ensuring all 16 ports worked.
The software comes with three demonstrational pieces of software that run under NBASIC:
The Model 3 Student station running Meteor Mission 2.
Thank you for reading, check the events page if you would like to see the exhibit in person or come meet us.