6502-Retro-Banked (Version 3)

This is version 3 of the 6502-Retro! design.

Core System

WD65C02 Processor
39.75 KB SRAM 0x0000-0x9EFF
256 Bytes IO 0x9F00-0x9FFF
64 x 8 KB Extended SRAM 0xA000-0xBFFF
4 x 16 KB ROM 0xC000-0xFFFF
AT22V10C Programmable Logic Device for address decoding
Power supply via USB-Mini connector
DS1813 - Reset supervisor
4 MHz System Clock
1.8432 MHz Baud Rate Clock

Peripherals

WD65C22 Versatile Interface Adaptor (VIA)
R6551 Rockwell UART Adapter
SN76489 Programmable Sound Generator
- Header connector for amplified speaker
F18A Video Display Processor - FPGA Emulating TMS9918A

ROM ALLOCATIONS

Bank 0: 6502-Retro! OS
- System menu
- Wozmon
- DOS Simple File System (SFS) a custom, minimal filesystem for use with the 6502-Retro!
  - Xmodem
Bank 2: ehBasic
- ehBasic is extended to support the following extra commands:
  - dir - File listing
  - load - Load a BASIC file from the SDCARD in raw ASCII listing form.
  - save - Save a BASIC file to the SDCARD in raw ASCII listing form.
  - beep - Emit a short beep from the speaker.
Bank 3: Hopper HS (https://github.com/sillycowvalley/Hopper)
Bank 4: smon6502 - https://github.com/dhansel/smon6502/tree/main

Memory Banking Logic

Memory banks are controlled by 2 write only registers. 0x9F00 for Extended RAM bank switching and 0x9F01 for ROM Bank switching. On reset these two registers are initialised to 0 which results in the main system being loaded on boot. Two ZeroPage addresses are reserved for maintaining a copy of the current value of the bank registers.

Serial Interface

By default, the OS is configured to support an FTDI type serial adapter with the following settings:

8 Data bits
1 Stop bit
No parity bit
115200 Baud
No Hardware flow control

IO Address Map

ADDRESS	DEVICE
0x9F00	RAM Bank Register (WRITE ONLY)
0x9F01	ROM Bank Register (WRITE ONLY)
0x9F10	ACIA Data
0x9F11	ACIA Status
0x9F12	ACIA Command
0x9F13	ACIA Control
---	---
9F20	VIA Port B
9F21	VIA Port A
9F22	VIA Data Direction B
9F23	VIA Data Direction A
9F24	VIA Timer 1 Counter Low
9F25	VIA Timer 1 Counter High
9F26	VIA Timer 1 Latch Low
9F27	VIA Timer 1 Latch High
9F28	VIA Timer 2 Counter Low
9F29	VIA Timer 2 Counter High
9F2A	VIA Shift Register
9F2B	VIA Auxillary Control Register
9F2C	VIA Program Control Register
9F2D	VIA Interrupt Flags Register
9F2E	VIA Interrupt Enable Register
9F2F	VIA PORT A (No Handshake)
---	---
0x9F30	F18A RAM
0x9F31	F18A Register