View source for Programmable Flash Memory Expansion

The PFM512 boot device modification replaces the standard 16KiB 28-pin boot EPROM with a 512KiB 32-pin Atmel 29c040 flash chip.  The chip is visible in four 128KiB banks residing at memory pages 0xF0 - 0xFF.  Each page is selected via two re-purposed (normally unused) TMS9901 outputs:

{| style="width:70%; margin-top:3ex"
|-
| colspan="4" style="background-color:lightgray; text-align:center" | PFM512 Bank Selection
|-
| style="width:15%; font-weight:bold" | CRU 0x28
| style="width:15%; font-weight:bold" | CRU 0x3A
| style="width:15%; font-weight:bold" | Bank
| style="font-weight:bold" | Notes
|-
| 0
| 0
| Bank 0 Default
| Boot code and Operating System
|-
| 0 
| 1 
| Bank 2
| Flashdisk bank #1
|-
| 1
| 0
| Bank 1  
| Flashdisk bank #2
|-
| 1
| 1
| Bank 3
| Flashdisk bank #3
|}