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IDT Device Controller
Device Read Transaction
79RC32438 User Reference Manual
6 - 13
November 4, 2002
Notes
When configured as a wait signal, WAITACKN must be asserted at least two clock cycles prior to the
end of
RWS.
WAITACKN assertions after this point are ignored. Thus, to use WAITACKN in this mode
RWS
must have a value greater than or equal to three.
Figure 6.10 Device Read Transaction
1
(WAITACKN Configured As Wait)
The WAITACKN signal may be configured as an Intel style wait signal or as a Motorola style transfer
acknowledge signal. Up to this point, this section has only considered WAITACKN configured as a wait
signal. When WAITACKN is configured as transfer acknowledge, then the read wait states (
RWS
) value is
ignored and the assertion of WAITACKN signals the completion of the transaction.
Figure 6.11 Device Read Transaction
1
(WAITACKN Configured As Transfer Acknowledge)
The device read transaction, with WAITACKN configured as a transfer acknowledge input, consists of
the following steps.
1. The RC32438 drives the address bus (MADDR[25:0]), drives RWN high and BDIRN low, and asserts
BOEN
2
on the rising edge of EXTCLK. This indicates the start of a transaction.
2.
CSD
clock cycles after step one, the RC32438 asserts the appropriate chip select (CSNx).
3.
OED
clock cycles after step one, the RC32438 asserts output enable (OEN).
4. The external device asserts WAITACKN once it has driven valid data onto the data bus and is ready
for the transaction to complete.
1.
The programmable parameters shown in this figure are for illustrative purposes only and may be varied.
2.
BOEN is only asserted if the buffer enable (BE) bit is set in the device control register (DEVxC).
EXTCLK
MADDR[25:0]
RWN
CSNx
BWEN[1:0]
OEN
MDATA[15:0]
Transaction
CSD
OED
RWS
CSH
Address Valid
Data Valid
Transaction
PRD
BOEN
WAITACKN
EXTCLK
MADDR[25:0]
RWN
CSNx
BWEN[1:0]
OEN
MDATA[15:0]
Transaction
CSD
OED
PRD
CSH
Address Valid
Data Valid
Transaction
BOEN
WAITACKN