User:Lidnariq/Mapper thoughts

EtherNES 1

A cartridge designed to provide ethernet is as simple a manner as practical, for use with Contiki. The design is intentionally similar to a C64 ethernet cartridge, even though the CS8900A is comparatively expensive.

Parts

• 1 × SST39SF010A, 128 KiB FLASH EEPROM, for booting
• 2 × AS6C1008, 128 KiB static RAM, one each for PRG RAM and CHR RAM
• 2 × 74'161, both set up to clear on reset.
  • One selects a 32 KiB slice of PRG
  • The other selects an 8 KiB slice of CHR RAM.
• 2 × 74'139
• 1 × 74'10
  • One NAND3 produces /INTSEL=NAND3(M2,/ROMSEL,A14) and one decoder produces /5xxx, /6xxx, and /7xxx.
  • Another NAND3 produces /RD.
  • 2nd decoder selects RAM or ROM as appropriate.
  • 3rd decoder produces /IOR and /IOW for CS8900A. (is cleverness possible to skip this somehow?)
  • Final NAND3=??
• CS8900A (or possibly RTL8029)
• Ethernet transformer

See also http://www.go4retro.com/products/64nic/

Memory map

• $5xxx - CS8900A
  • http://www.cirrus.com/en/products/cs8900a.html
  • As with the C64 NIC, it does not present the memory-mappable portion of the CS8900A
  • CS8900A does not have a separate I/O enable, just /IOR and /IOW; address bus must be stable before these signals fall.
  • Why does the 64NIC+ not connect /IRQ ?
  • Obviously no DMA support either. (Do we want to support OAM DMA from ethernet?)
• $6xxx - PRG bank '161 (0,1,2,3 = ROM; C,D,E,F=RAM). Q3 determines which IC. Cleared on hardware reset.
• $7xxx - CHR '161
• $8000-$FFFF: PRG ROM or RAM, according to value at $6xxx.