Datasheet

ADuC7128/ADuC7129
Rev. 0 | Page 84 of 92
The XMxPAR are registers that define the protocol used for accessing the external memory for each memory region.
Table 121. XMxPAR MMR Bit Designations
Bit Description
15
Enable Byte Write Strobe. This bit is only used for two,
8-bit memory sharing the same memory region.
Set by user to gate the AD0 output with the WS output. This allows byte write capability without using
BHE and BLE signals.
Cleared by user to use
BHE and BLE signals.
14:12 Number of Wait States on the Address Latch Enable Strobe.
11 Reserved.
10 Extra Address Hold Time.
Set by the user to disable extra hold time.
Cleared by the user to enable one clock cycle of hold on the address in read and write.
9 Extra Bus Transition Time on Read.
Set by the user to disable extra bus transition time.
Cleared by the user to enable one extra clock before and after the read select (
RS).
8 Extra Bus Transition Time on Write.
Set by the user to disable extra bus transition time.
Cleared by the user to enable one extra clock before and after the write select (
WS).
7:4
Number of Write Wait States. Select the number of wait states added to the length of the
WS pulse. 0x0 is 1 clock cycle; 0xF is 16 clock
cycles (default value).
3:0
Number of Read Wait States. Select the number of wait states added to the length of the
RS pulse. 0x0 is 1 clock cycle; 0xF is 16 clock
cycles (default value).
TIMING DIAGRAMS
Figure 62 through Figure 65 show the timing for a read cycle (see Figure 62), a read cycle with address hold and bus turn cycles (see
Figure 63), a write cycle with address hold and write hold cycles (see Figure 64), and a write cycle with wait states (see Figure 65).
06020-069
HCLK
A
D16:0
ADDRESS DATA
MSx
AE
RS
Figure 62. External Memory Read Cycle