TRS-80.org

Christmas 2008 issue of TRS8BIT newsletter

Matthew Reed — Mon, 22 Dec 2008 19:26:22 +0000

If you haven’t stopped by trs-80.org.uk lately, then you might not know that Dusty has released a new Christmas edition of his TRS8BIT newsletter. Among other things, this issue includes a Sudoku creation program converted to the TRS-80 by Peter Phillips. If you’re interested, you can download the current issue or any of the seven other issues.

CHROMAtrs

Matthew Reed — Fri, 19 Dec 2008 22:39:29 +0000

Probably the most popular of the TRS-80 Model I and III color add-ons was the CHROMAtrs, sold by South Shore Computer Concepts starting in 1982. It was available in several configurations:

a kit without case or power supply cost $99
a kit with case and power supply cost $129
a fully-assembled and tested unit cost $169.

Each CHROMAtrs unit supported both the Model I or Model III and would work with either computer using the proper cable. The Model III cable would also work with the Lobo MAX-80 with a few minor modifications.

The Percom Separator

Matthew Reed — Tue, 16 Dec 2008 17:26:36 +0000

The Radio Shack Expansion Interface added single-density floppy disk support to the TRS-80 Model I. Floppy disks were a great improvement over cassettes. But many people reported problems with reliability, particularly when reading or writing lower disk tracks. CRC errors and locked out tracks occurred with disturbing regularity.

The Separator, sold by Percom for $29.95, fixed all of those problems. It provided a data separator with far higher resolution (16 MHz) than the separator used by the Expansion Interface (1 MHz). Good data separation was vital for isolating the clock and data pulses that made up a disk track.

Model 4 emulation card: Fact or fiction?

Matthew Reed — Tue, 09 Dec 2008 18:02:39 +0000

After Radio Shack introduced their MS-DOS compatible Model 1000 series, there were persistent rumors about a Model 4 emulation card that was being developed. Such a board would have been an clever way to help migrate Model 4 customers to the newer MS-DOS computers. Some people were even told at their Radio Shack stores that a Model 4 emulator would be released soon. But it never happened and no type of TRS-80 emulator was ever released by Radio Shack.

At the time, Radio Shack sold the Trackstar, an Apple IIe emulator card created by Diamond Computer Systems. The Trackstar used actual Apple II ROMs (licensed from Apple) along with custom hardware to achieve nearly 100% Apple compatibility. So the concept of a Model 4 emulation card certainly must have occurred to people at Radio Shack.

I’ve had three different people write to me (years apart) recalling details of a Model 4 emulation project that Radio Shack worked on but pulled at a very late stage. Their accounts match in almost all the details.

Electric Crayon

Matthew Reed — Mon, 08 Dec 2008 15:47:18 +0000

Back in the late 1970’s, the Apple II and the TRS-80 Model I were fierce competitors for computer sales. One advantage the Apple II had over the Model I was the ability to display color graphics. The first product to address this perceived Model I deficiency was the Percom Electric Crayon. Percom introduced the Electric Crayon in December 1979 for a base price of $249. It was featured on the cover of the January 1981 issue of 80 Microcomputing.

The Electric Crayon was a small (12 inch wide by 9 inch deep) box which output a composite video signal that could drive either a monitor or a television set. It connected directly to the TRS-80 printer port and was controlled using EGOS, a ROM-based operating system. EGOS was directly programmed using single character commands. Unique among TRS-80 color add-ons, the Electric Crayon did not use the TMS9918 graphics chip and did not support sprites.

What does S-80 mean?

Matthew Reed — Sat, 06 Dec 2008 02:50:02 +0000

The term “S-80” sometimes appeared in advertisements and articles as a synonym for “TRS-80”. Most often it was used to refer to the TRS-80 expansion bus (“S-80 bus”). Other times it was an all-encompassing term for the TRS-80 and compatibles (“S-80 computers”). Another example was the newsletter S-80 Computing which described itself as a “monthly newspaper supporting the TRS-80”.

I had wondered about the origins of the term, but I found this definition in the March/April 1980 issue of 80 U.S. Journal:

Mikeegraphic Graphic System

Matthew Reed — Wed, 03 Dec 2008 02:15:43 +0000

The Mikeegraphic Graphics System was a high-resolution graphics add-on for the TRS-80 Model I and Model III. It was sold by Mikee Electronics Corporation for $340. Originally known as the Mikeeangelo when it was introduced in late 1981, the name was changed to Mikeegraphic just a few months later, presumably to avoid confusion with another product.

Unlike the 80-GRAFIX, which provided high-resolution using a programmable character generator, the Mikeegraphic used a true bitmapped graphics screen. The high-resolution screen was mapped in its entirety at the top of the TRS-80 memory.

Volume Setting - The Cassette Gazette Page 8

Matthew Reed — Thu, 27 Nov 2008 22:22:29 +0000

From page 12 of the Cassette Gazette:
There are two signal types used for TRS-80 cassette storage: ‘Pulse’ (Model I & III 500 baud and Model I 2x-6x KWIK), and ‘FSK’ (Model III 1500 baud and 2200 baud). Let’s not get into the technical reasons ‘why’, but we use the following thumb rules for setting the CTR playback volume:

‘Pulse’, with a LemonAid Loader: Leave the volume full up; adjustment is automatic.
‘Pulse’, without a Loader: Set the volume a little above the mid-point of the useable loading range. The 500 baud ‘useable’ range is found empirically (plain old trial-and-error method); the KWIK 2x-6x range can easily be determined during leader ‘lock-on’. In either case the range will vary with different tapes.
‘FSK’: Full up. (Yes… full up!)

Note: The setting of the volume control has NO effect whatever on the recording level. (Try it!)

TRS-80 XRX Mod - The Cassette Gazette Page 7

Matthew Reed — Wed, 26 Nov 2008 16:22:46 +0000

From the Cassette Gazette page 7:
We love our TRS-80’s, and will always be grateful to Tandy for providing us with this wonderful machine!

But nothing is perfect, and for good reasons the early Model I units earned a reputation for “dismal” cassette performance. The real problem was NOT the fault of the hardware, however. The CTR-80/80A (also its predecessor, the CTR-41) and the cassette port circuitry are excellent, and capable of far better than the 500 baud standard chosen by Radio Shack. Non-uniform head alignment and very poor quality ‘commercial’ duplication of program tape contributed to the problem, but the most important fault was in the ROM… the coding that set the timing loops for tape loading was simply incorrect. Radio Shack corrected the timing in the ‘new’ ROMs used in later machines, but they were not about to replace the ROMs in all the early units.

“Pinch Hits” & “Switch Hits” - The Cassette Gazette Page 6

Matthew Reed — Tue, 25 Nov 2008 16:51:55 +0000

From page 6 of the Cassette Gazette:
When a program tape develops a fault it is usually called a “hit”. One common type is a “switch hit”, which is a sharp spike of noise placed on the tape when the motor current stops suddenly. If you switch off your recorder in the middle of a program, or if the program bombs and the computer turns the recorder off, any switch hit that occurs will make that copy forever unloadable. A capacitor or diode or both across the CTR motor can help this problem... but we, of course, think we offer a better solution.

The SOFTROL is a solid state switch that has a built-in one-second motor off delay. The power to the motor is reduced slowly to bring it to a “soft” stop, instead of cutting it off abruptly.

But the motor off delay does more than just stop switch hits... the extra one seconds pulls the tape nearly two inches beyond the point where the recorder gets the signal that the program is through. This pulls the end of the program out from between the pinch roller and capstan of the recorder. Without this action (unless you always remember to release the recorder PLAY button), the end of the program is being squeezed continuously. This can put a dimple on the tape that busts the load... a pinch hit... just before the end of the program.