Single Read Transfer; Figure 16-3. Single Read Transfer - IBM PowerPC 405GP User Manual

• The hold time, EBCO_BnA.P[TH], is programmable from
°
to 7 PerClk cycles. During the hold time
the peripheral address bus remains driven with the last address and all control signals are actively
driven high. If the operation was a write, the peripheral data bus continues driving the last data
value.
• There is no guarantee of dead cycles between transfers on the peripheral interface. If there are
back-to-back transfers to the same memory bank and the number of hold cycles is programmed to
zero (EBCO_BnAP[TH]=O) and EBCO_BnAP[CSN]=O, then:
- PerCSn may not go inactive between the back-to-back transfers.
- If EBCO_BnAP[DEN]=O, PerDE may not become inactive between the two transfers.
- If EBCO_BnAP[WBN]=O'and EBCO_BnAP[WBF]=O, PerWBEO:3 may not go inactive between
the back-to-back transfers.
16.2.1 Single Read Transfer
Figure 16-3 shows the peripheral interface timing for a single read transfer from a non-burst enabled
(EBCO_BnAP[BME]=O) bank. The transaction begins with the address being driven. Since this is a
single transfer, PerBLast is also driven active along with the address. If byte enable mode is enabled
for the bank (EBCO_BnAP[BEM]=1) the byte enables are also output concurrently on PerWBEO:3.
PerCSn then becomes active EBCO_BnAP[CSN] cycles after the address, while PerDE goes low
EBCO_BnAP[DEN] cycles after PerCSn. The EBC then waits until EBCO_BnAP[TWT]+ 1 cycles have
elapsed since the start of the transaction and then reads the data bus and the peripheral error input,
PerErr. If parity checking is enabled (EBCO_BnAP[PAR]=1) the parity is also read at this time. The
EBC then drives PerCSn, PerDE and PerBLast high and waits EBCO_BnAP[TH] cycles.
Cycle
[IJj
to to to
trn:=
PerClk
M~V1V1Wl-,
l
! :
l l ; !
I
I
!
PerAddrO:31 r::;J~~Ad~d-res-s~--iC
:
~TWT+1-+j
TU
I
i
'~I ~I
percsn~
PerRiW
R
~
!
R
PerOE~
PerBLast
H i '
r--t:::
[
perwBEo:3
[ 3 • . ; ' . . . . . ' .
LJ
BEM=O :. , I
i
PerWE
~c=J-
..
~.r-~~~--~~-
...•
~:
[
PerWBEO:3
rz::::J.,.> . . . . ,
~--=BE=--~--id
BEM=1 ' ,
PerWE -c:J~'·'~·'-~i~--~-r\iJ~···'~j
: !
i i i i
pe~~~~~~~~
. PerErr
~~~~~~
Figure 16-3. Single Read Transfer
16-6 PPC405GP User's Manual