NEO-273



This chip is used in cartridges to replace 74LS273 and 74LS174 latches that were used in early boards (Like on CHA-32). It demultiplexes the P bus to C ROM and S ROM addresses.

It includes one 16-bit latch (to address a 128KiB S ROM) and one 20-bit latch (to address 8MiB of 2*16bits C ROMs) in one package. Note that A4 ("CA4") of the C ROMs and A3 ("2H1") of the S ROM are not part of the multiplexed bus and come straight from the cartridge edge, bypassing this chip.

This chip was later replaced by NEO-CMC which performs the same function along with quite a few other things.

For cartridges that use this chip but have more than 8MiB of C ROM, extra bits were added using 7400 chips. An added LS74 (2 bits) in CHA256 boards for example increases the C ROM capacity from 8MiB to 32MiB (256M).

Demultiplexing
=Pinout=

Pin 47 might be /C_A20 (used for upper /CE on CHA 42G-1)



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