This chapter describes the Boot PROM.
The Boot PROM, U0402 on the lower board scematic, is a 64K-byte read-only memory that stores identification data that is unique to each Board.
The Boot PROM is a 64K by 8-bit reprogrammable read-only memory. The Boot PROM is accessed from LeoCommand, for either reading or reprogramming. As shown in Figure 12-1, the Boot PROM uses signals from both the CD Bus and the CX Bus. The CD Bus provides the PROM address, the CX Bus carries the PROM data.
Figure 12-1 Boot PROM Interface Block Diagram
To read the contents of the PROM, LeoCommand places the address on the CD_DAT<15:0 lines and drives the PROM_CS_L signal low. The contents of the memory location addressed by the CD_DAT<15:0 lines becomes available on the CX_DAT<7:0 lines. Figure 12-2 shows the read timing.
Figure 12-2 Boot PROM Read Timing
To reprogram the contents of the PROM, the VPP line must be enabled by adding a jumper to the board (J1101 on lower board schematic). This enables +12 volts (PROM_VPP) to the PROM VPP input. The jumper must be removed for normal board operation.
During the reprogram cycle, LeoCommand drives the CX_R_WL signal (the Flash input to the PROM) low, places the address on the CD_DAT<15:0 lines, places the data on the CX_DATA<7:0 lines, and drives the PROM_CS_L signal low. Figure 12-3 shows the reprogram timing.
Figure 12-3 Boot PROM Reprogram Timing
