Signal Multiplexing

Depending on the byte access type (BAT), only the byte write signals or the byte select signals are used. To save I/Os at the external bus interface, control signals at the SMC interface are multiplexed. The following table shows signal multiplexing depending on the data bus width and the byte access type.

For 16-bit devices, bit A0 of address is unused. When the Byte Select option is selected, NWR1 is unused. When the Byte Write option is selected, NBS0 is unused.

Table 1. SMC Multiplexed Signal Translation
Device Type Signal Name
16-bit Bus 8-bit Bus
1 x 16-bit 2 x 8-bit 1 x 8-bit
Byte Access Type (BAT) Byte Select Byte Write
NBS0_A0 NBS0 A0
NWE_NWR0 NWE NWR0 NWE
NBS1_NWR1 NBS1 NWR1
A1 A1 A1 A1