Read Only Memories used in ZX Spectrum machines.
16Kx8 bit MASK programmable ROM chip
1 of this IC make the ROM of the ZX Spectrum 16K/48K.
e.g. NEC UPD23128 or Hitachi HN613128P
1 ° 28
The NEC ROM pin names in paranthesis.
On the PCB there are four hole and two link. The position of the links depend from the ROM IC type (Hitachi or NEC):
O - (N) - O | | H H | | O - (N) - O
The Hitachi (H) and NEC (N) ROMs use different pins for the enable and select inputs (i.e. pins 20 and 27). The links allow the inputs to be reversed accordingly.
- Pin22 OE0/(OD) connected to Z80 RD
- NEC Pin20 and Hitachi Pin27 OE/OE1 connected to Z80 MREQ
- NEC Pin27 and Hitachi Pin20 CS connected (with a 680 ohm resistor) to ULA ROMCS