X-Mem/80 TRS-80 Model I memory upgrade

X-MEM/80 is a 512 KB paged memory expansion for the TRS-80 Model 1 and Model III.

It is partially SuperMem compatible, as it allows to "bank" the upper 32 KBs (address range from 0x8000 to 0xFFFF) with the memory on the card.

A jumper allows configuration in two different modes - SuperMem and X-MEM/80 modes:

• in SuperMem mode, it offers 16 pages of 32 KBs, which are mapped into the 0x8000 to 0xFFFF (= upper 32 KB) range. To select the page number, out 67,<page number> is used. The page number can also be read back via inp 67. Unlike SuperMem, X-MEM/80 does not allow to bank the lower 32 KBs of the Model 1 memory. However, the existing SuperMem software (see below) doesn't seem to use this mode anyway, and works fine with X-MEM/80's SuperMem mode.
• in X-MEM/80 mode, it offers 32 pages of 16 KBs, which can be mapped to the lower and higher 16 KB page of the upper 32 KB range, i.e., the lower 16 KB page from 0x8000 to 0xBFFF and the higher 16 KB page from 0xC000 to 0xFFFF. To select the lower 16 KB page, out 65, <lower page number> is used, and out 66, <higher page number> for the higher 16 KB page. Note that it is possible to map the same pysical 16 KB page into both the lower and higher address range (but this is usually not desirable).

(This was designed by lambdamikel on Github, produced by a 3rd party PCB facility, and used with permission)