IBM PowerPC 405GP User Manual

signals can transition from the active state to high-Z without first being driven inactive. To prevent this,
all peripheral banks must be configured with at least one hold cycle, EBCO_BnAP[TH] > 0.
Table
16-2. Effect of Driver Enable Programming on EBC Signal States
ExtReset
PerClk PerAddrO:31
PerWE PerRIW
HoldAck
PerWBEO:3
EBC BusReq PerCE PerDataO:31
Operation
ExtAck PerCSO:7
PerBLast PerParO:3
Reset High-Z High-Z High-Z High-Z
Idle Driven EBCO_CFG[CSTC] EBCO_CFG[EBTC]
EBCO_CFG[EBTC]
Read
Driven Driven
Driven
High-Z
Write
Driven
Driven Driven Driven
External Master Driven EBCO_CFG[CSTC]
High-Z
High-Z
Note 1: If the EBCO_CFG bit is set, the signal is driven to the appropriate state during the indicated
EBC operation. Otherwise, the liD is High-Z.
16.2 Non-Burst Peripheral Bus Transactions
The timing of the PerCSn, PerDE, and PerWBEO:3 signals is programmable via the Peripheral Bank
Access Parameter
(EBCO_BnAP) registers. For non-burst transfers, the access parameter registers
control the peripheral bus timing as follows:
• PerCSn
becomes active 0-3 PerClk cycles (EBCO_BnAP[CSN]) after the address is driven.
• 'P8rOE is driven low 0-3 PerClk cycles (EBCO_BnAP[OEN]) after PerCSn is active.
• PerBLast is active throughout the entire transfer and is driven high during the programmed hold
time (EBCO_BnAP[TH]).
• PerWBEO:3 can be either write byte enables or read and write enables.
If EBCO_BnAP[BEM]=O,
PerWBEO:3 are write byte enables and:
- PerWBEO:3 goes active
0-3 (EBCO_BnAP[WBN]) PerClk cycles after PerCSn becomes active.
- PerWBEO:3 becomes inactive
0-3 (EBCO_BnAP[WBF]) PerClk cycles before PerCSn becomes
inactive.
If EBCO_BnAP[BEM]=1, PerWBEO:3 are readlwrite byte enables and have timing identical to the
peripheral address bus. In this case the EBCO_BnAP[WBN] and EBCO_BnAP[WBF] parameters
are ignored.
• 1-256 PerClk cycles (EBCO_BnAP[TWT] + 1) after the address became valid:
- If EBCO_CFG[CSTC]=1 or EBCO_BnAP[TH]>O, PerCSn is driven high.
-
If EBCO_CFG[CSTC]=O and EBCO_BnAP[TH]=O, PerCSn transitions directly from logic ° to the
high-impedance state.
• The parameters TWT, CSN, DEN, WBN, and WBF in EBCO_BnAP are not independent. For non-
burst configured banks it is required that TWT ~ CSN + MAX(OEN,WBN) + WBF.
External Bus Controller 16-5

IBM PowerPC 405GP Specifications

General

Brand	IBM
Model	PowerPC 405GP
Category	Computer Hardware
Language	English