Flash Eeprom - Rastergraf Topaz User Manual

Rastergraf

5.12 Flash EEPROM

The graphics board has a 128 KB Flash EEPROM. It can be updated in the
field using a special updater program. The code in the PROM cannot be
directly executed by the CPU. It must be read by the host CPU into its
memory and executed from there.
The SM731 accesses the PROM data through the SDRAM data port. The
multiplexed address bits contain both the high and low order address lines
for the PROM. The high order lines appear first and so must be latched
externally.
Although in most cases the standard BIOS PROM would be 32 KB, a 128
KB is used on the Graphics board in order to accommodate multiple BIOS
images (not currently implemented).
The way to go into the special PROM mode is this:
1) Program the SM731 chip to external bus, no refresh, mclk2 = 25MHz.
2) Read from prom location 0x990 (bits 12:4 = 0x99, rest don't care).
3) Read from prom location 0x660 (bits 12:4 = 0x66, rest don't care).
4) Set bit 3 at memory location 4 (bit 35 with dqm0 = false).
5) Write PROM address [16,1,0] at memory location 4 (with bit 3 set).
6) Read the PROM data.
7) To write PROM data, follow the memory location 4 write with a
memory location 3 write of the data. The next PROM read will write the
PROM with the data. To return to the read mode, write memory location 4
again.
8) To exit the special mode, clear bit 3 of memory location 4.
5-30 Programming On-board Devices and Memories