Memotech Limited MTX 500 User's Guide download pdf (Page 21)

MTX500 JUMPER

Earlier MTX500s had a memory decoder PAL which made pages of the 32KB of memory appear in

more than one place in the memory map. You can replace the PAL with a GAL which ensures the

pages appear only once. Later MTX500s had a PAL which did this, and its entirely safe to make this

change whether or not you plan to use REMEMOrizer. But REMEMOrizer can only work with

MTX500s that only present the pages once. Therefore, if you have a MTX500, replace the PAL with

the 2_32 or 3_32 GAL supplied with REMEMOrizer. The 2_ or 3_ prefix refers to how many ROMs

you have. Even if you don't always use REMEMOrizer, you can leave this new GAL installed.

Technically, if you know you have the newer variety of MTX500, you needn't replace the PAL, but

rather than describe the process of telling the difference, and expecting the user to follow it, its

simpler to change the chip and be sure.

If your MTX only has 32KB of RAM, set the MTX500 jumper "high". This causes REMEMOrizer to

provide a RAM upgrade, using 32KB of its SRAM.

If your MTX has 64KB of RAM, set the MTX500 jumper "low".

Warning: Do not set the jumper "high" if your MTX has 64KB of RAM, or if you have not

replaced the PAL in your MTX500. Both the motherboard and REMEMOrizer will attempt to

drive the bus when the top 32KB of RAM is accessed, which could result in permanent

damage to the MTX and/or REMEMOrizer.

Note: If, have a partially upgraded MTX500, you may have an MTX000, i.e.: a MTX with no memory at

all! If the MTX500 jumper is "high" and the ROMs jumper is also "high", then the modified OS ROM

will notice the lack of memory and tell REMEMOrizer to also provide the lower 32KB RAM.

MTX512 S2

If you have an MTX512 S2, then your motherboard will have 4256 DRAMs and a different memory

decoder PAL. This PAL makes 64KB available in RELCPMH=0 mode and 208KB available in

RELCPMH=1 mode. 144KB of the memory in RELCPMH=1 mode will clash with memory provided

by REMEMOrizer.

Therefore, if you have a an MTX512 S2, replace the PAL with the 2_64_s2 GAL supplied with

REMEMOrizer. As all MTX512s had 2 ROMs, there is no 3_64_s2 GAL. This GAL only makes 64KB

memory available in RELCPMH=1 mode.

Warning: Do not attach REMEMOrizer to an MTX512 S2 if you have not replaced the PAL. Both

the motherboard and REMEMOrizer will attempt to drive the bus when high memory is

accessed, which could result in permanent damage to the MTX and/or REMEMOrizer.

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Memotech Limited MTX 500 User's Guide Page 21