1. The PULL rear connector is repeated so other accessories can be used, including a bank switching controller and back-plane.
2. Use two 28 pin sockets for “HOME ROM” and two for “EXROM”. That way you can use RAM chips before burning EPROM’s. You can plug in a direct replacement for 6264 RAM, but not 43256.
3. When using EPROM, a 27128 chip can be used for “HOME ROM”, leaving one socket empty.
4. When using ROM for “EXROM”, use 43256 chips for reasons of economy. (32K*8bits)
5. “EXROM” memory from 0 to 32K is assumed to be 43256 “ROM” or 27256 EPROM. (See Pig. 2a,c)
6. Write-protect switches are used when RAM takes the place of ROM. One covers “HOME ROM”, the other CHUNKS #0 thru #3 of “EXROM”.
7. Other switches allow RAM to be initialized (written) before being configured as “ROM”. This allows HOME ROM and EXROM to be copied to external RAM.
8. A jumper is provided to eliminate battery backup once EPROM has been installed in place of write-protected “HOME” ROM.
Because bypass operations need BE to operate, and external banks have higher priority, the board must monitor BE’ to avoid conflict. The circuit shown breaks into the BE signal line to make this possible.
The average user wants better operation, more memory, more gadgets and software which makes use of them. who can blame them, but not everyone has the technical knowledge and skill to do it on their own.
The design presented here is hereby declared PUBLIC DOMAIN, with the blessings of The WIDJUP co. Suppliers are free to manufacture, but it is strongly suggested that The WIDJUP co. be consulted when doing 80.
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PROCEDURE | S1 SWITCH SETTINGS | NOTES |
==========================| a b c d e f |===================|
NORMAL OPERATION: |===========================| ROM/EPROM EPROM |
"HOME": | | 0-8,8-16K; 0-16K |
Using EPROM | ON ON OFF (Fig 1) | (PGM High) |
Using RAM as "ROM" | ON ON OFF (Fig 1) | 0-16K Read Only |
"EXROM": | | 0-32,32-64K;0-32K |
Using EPROM & RAM | (Fig 2c) --- --- --- | 32-64K RD/WR |
Using RAM as "ROM" | (Fig 2a) ON ON ON | 0-32K Read Only |
EXROM Removed | (Fig 2b) --- ON OFF | 0-32K Read Only |
--------------------------|---------------------------|-------------------|
COPYING INTERNAL ROM: | | |
HOME to "HOME" RAM: | OFF OFF ON (Fig 1) | Write Only 0-16K |
EXROM to "EXROM" RAM: | (Fig 2a) OFF OFF OFF | Write Only 0-8K |
EXROM to EPROM ROM: | (Fig 2c) --- --- --- | Done Externally |
EXROM Removed | (Fig 2b) --- OFF ON | Before removal |
--------------------------|---------------------------|-------------------|
MAKING "ROM" CHANGES: | | |
"HOME": | ON ON ON (Fig 1) | Read/Write 0-16K |
"EXROM": | (Fig 2a) ON ON OFF | Read/Write 0-32K |
EPROM: | (Fig 2c) --- --- --- | Done Exterally |
EXROM Removed | (Fig 2b) --- ON ON | Read/Write 0-32K |
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This Bypass Design Stands Alone.
Nevertheless, RGB video, analog signals, external power sources, bus re-powering and attachment of back-planes are features best located on the same board. Provisions for adding features would satisfy those not yet ready for slot expansion.
It is quite easy to copy internal ROM to the bypass board.
10 REM Fig 1: HOME ROM
20 FOR N = 0 TO 16383
30 POKE N, PEEK N
40 NEXT N
---------------------------------
10 REM Fig 2a,b: EXROM
20 SAVE "EXROM" CODE 0, 8196
30 LOAD "EXROM" CODE 0, 8196Once an updated operating system is available, the most convenient way to operate is with a combination of Figure 1 (with a single 27128) and Figure 2c. The switches and battery backup can be eliminated. All you need are the proper EPROMs and board. The TS2068 will still operate without the board attached. If you like to change operating systems, like using SPECTRUM or CP/M, So you COULD have a set of EPROMs for each. This requires no special knowledge or procedures. There is, however, another way.
If you like to try your hand at making operating system changes by yourself, you can.
If you prefer to simply load one of several operating systems provided by others, you can.
[Figure: Figure 2c: EXROM Bypass / EPROM, circuit schematic, (C) 1988 William J. Pedersen]
The combination of Figure 1 and Figure 2a can hold any operating system including the original. Using a fairly simple procedure which can be prompted by a loaded program, any operating system can be “booted” into the TS2068 as software, just like other computers do.
The switches on the board are hardware in the figures, but they could easily be operated by I/O, making booting entirely automatic.
Once a system has been booted, you don’t have to repeat it every time you turn your computer off and on. Who said the TS2068 is an orphan?
It is probably best to explain a little bit about how these circuits work without getting too technical.
If you ever tried writing to ROM, you know nothing happens. All you can do is read from it. These boards have STATIC RAM covering the same address space as ROM. That CAN be written to. you just have to be careful not to read anything back or confusion reigns. This is solved by a switch which prevents reading from RAM.
It is interesting that a program can be running in ROM at the same time it is being “written to”. There is no interference. In fact, the ROM program can make a copy of itself in RAM, down to the last detail.
Ah hah! Now we can switch from ROM to RAM, switch the RAM to read-only, and you can’t see anything different—so why do it?
You wouldn’t, of course. Why copy ROM code when you can do better? The only reasons you might are to check out the hardware and to get a head start on making your own code modifications.
The rest of the circuitry makes sure that not only will your present programs run without changes, but that features TIMEX left out WILL. It will if you want, that is. Should you want FORTRAN, Pascal, FORTH, or something else instead, it is possible. The TS2068 hardware is a marvel of design. It lends itself to bank-switching for large memory capacity. It has no inherent problems with time-sharing. It is fast. It has no problem working with an expansion back-plane, DMA, nor other bus masters.
It Can Even Run IBM & Clone Accessories!