Programmable Flash Memory Expansion
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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:
| PFM512 Bank Selection | |||
| CRU 0x28 | CRU 0x3A | Bank | 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 |