The MITS price list includes two boards the 88-RMB ROM BASIC I and 88-RMB2 ROM BASIC II. The Jan 78 MITS memo ROM BASIC Operation mentions the "Preliminary" 16K Extended ROM BASIC Board.
The 88-RMB ROM BASIC I board does not have auto-start logic and was used in conjunction with the Turnkey Module board. My assumption is that the 88-RMB ROM BASIC I board would work in a front panel machine without a Turnkey board.
I assume the 88-RMB2 ROM BASIC II has auto-start logic. I've only seen examples for the 88-RMB ROM BASIC I board. Does anyone know if the 88-RMB2 ROM BASIC II board was actually produced? The 88-RMB ROM BASIC I board is fairly rare.
Another assumption is that the ROM BASIC board was intended for the Attache and died at the same time. The Attache did not sell well and Pertec focused on BASIC for business disk systems.
The memo "ROM BASIC Operation" and "Preliminary Attache User's Manual" provide a small amount of information:
ROM BASIC may be supported by an ACR (audio cassette recorder) for storing and loading of data only. ROM BASIC is the same Extended BASIC as on the disk without special disk functions.
Note: The ACR board used in the Attache was the 88-UIO.
To load BASIC from ROM, proceed as follows:
a) ROM BASIC does not dump into RAM memory; therefore it is actually not loaded in the normal sense. ROM BASIC occupies the top 16K of memory, and care must me taken to ensure that the turnkey PROM and RAM addresses do not conflict with ROM BASIC or other memory boards.
b) PROM and RAM addresses must be below 140000(octal), and not conflicting with other memories. Note: A Turnkey Module in a MITS 300 system would occupy the top 16K of memory.
On turnkey boards without the 88-SYS-CLG mod
, set the position of the 1K RAM block just above whatever the rest of RAM may be in the system. Note: A turnkey board with the 88-SYS-CLG modification has the 1K of RAM disabled. The RAM was removed on the latest board revision.
Note: For example, a 32K system becomes 33k with an unmodified early revision turnkey. Maximum RAM would 46K + 1K from turnkey + 1K of PROM. A modified turnkey might allow 47-48K RAM. The 88-SYS-CLG makes the PROMS phantom and 48K RAM may be possible.
Set the PROM address to just below ROM BASIC at 47K. Note from memo: Any Proms on the Turnkey Module can no longer be used.
Note: My assumption is the MITS PROMS cannot be used because they were coded to be in the top 16K. My assumption is that custom proms could be used.
c) SIO address 020 (octal)
Note: This is the standard MITS console port. The port could be on a turnkey board or 88-2SIO. Watch for address conflicts if you have both boards.
d) Start address 140000 (octal).
Note: 140000 (octal) would be the start address set on the turnkey or address switch settings on a front panel.
ROM BASIC runs in ROM at the top 16K of memory. After starting BASIC using an 88-SYS-CLG modified Turnkey Module, an OUT to port FF should disable the PROMs at 47K. BASIC starts at 0 and checks up until memory cannot be changed. R/O memory indicates a gap, PROM or ROM. With the PROMs disabled BASIC can find the RAM that overlapped before the OUT to FF. That assumes there are no gaps in RAM below the Turnkey Module.