Links to RSS and SB9600 info
- , pdf?
- , pdf?
Links to projects using Raspberry Pi RP2040 chip for ROM emulators:
Xcat Links
X9000 memory and code plug maps
The A14 and A15 address lines plus WR/ are attached to U506 chip select decoder.? I'm assuming the "real" part number is 74xx139.
Based on this the first section's input pins 1G/ (pin 1), 1A (pin 2), and 1B (pin 3) decode as
1Y0 (pin 4) decodes 0x0000 -> 0x3fff (n/c)
1Y1 (pin 5) decodes 0x4000 -> 0x7ffff (n/c)
1Y2 (pin 6) decodes 0x8000 -> 0xbfff - CS/ to U502 (EEPROM)
1Y3 (pin 7) decodes 0xc000 -> 0xffff - CS/ to U501 (EPROM)
The second section's input pins 2G/ (pin 15), 2A (pin 14), and 2B (pin 13) decode as
2Y0 (pin 12) decodes 0x0000 -> 0x3fff (n/c)
2Y1 (pin 11) decodes 0x4000 -> 0x7ffff - CE/ to U503 latch
2Y2 (pin 10) decodes 0x8000 -> 0xbfff - (n/c)
2Y3 (pin 9) decodes 0xc000 -> 0xffff - CE/ to U504 latch