Rainbow Electronics AT91CAP9S250A - Manual (Page 175)

175
6264A–CAP–21-May-07
AT91CAP9S500A/AT91CAP9S250A
Figure 22-7. Connection of 2x16-bit Data Bus on a 32-bit Data Bus (Byte Select Option)
22.8 Standard Read and Write Protocols
In the following sections, the byte access type is not considered. Byte select lines (NBS0 to
NBS3) always have the same timing as the A address bus. NWE represents either the NWE sig-
nal in byte select access type or one of the byte write lines (NWR0 to NWR3) in byte write
access type. NWR0 to NWR3 have the same timings and protocol as NWE. In the same way,
NCS represents one of the NCS[0..5] chip select lines.
SMC
NWE
NRD
NCS[3]
Write Enable
Read Enable
Memory Enable
NBS0
D[15:0] D[15:0]
D[31:16]
A[25:2] A[23:0]
Write Enable
Read Enable
Memory Enable
D[31:16]
A[23:0]
Low Byte Enable
High Byte Enable
Low Byte Enable
High Byte Enable NBS1
NBS2
NBS3
Table 22-3. SMC Multiplexed Signal Translation
Signal Name 32-bit Bus 16-bit Bus 8-bit Bus
Device Type 1x32-bit 2x16-bit 4 x 8-bit 1x16-bit 2 x 8-bit 1 x 8-bit
Byte Access Type (BAT) Byte Select Byte Select Byte Write Byte Select Byte Write
NBS0_A0 NBS0 NBS0 NBS0 A0
NWE_NWR0 NWE NWE NWR0 NWE NWR0 NWE
NBS1_NWR1 NBS1 NBS1 NWR1 NBS1 NWR1
NBS2_NWR2_A1 NBS2 NBS2 NWR2 A1 A1 A1
NBS3_NWR3 NBS3 NBS3 NWR3