AM79C976 Advanced Micro Devices, AM79C976 Datasheet - Page 39

• Manufacturer Part Number: AM79C976
• Description: PCnet-PRO 10/100 Mbps PCI Ethernet Controller
• Manufacturer: Advanced Micro Devices

When the Am79C976 controller is not the current bus
master, it samples the AD[31:0], C/BE[3:0], and the
PAR lines during the address phase of any PCI com-
mand for a parity error. When it detects an address par-
ity error, the controller sets PERR (PCI Status register,
bit 15) to 1. When reporting of that error is enabled by
setting SERREN (PCI Command register, bit 8) and
PERREN (PCI Command register, bit 6) to 1, the
Am79C976 controller also drives the SERR signal low
for one clock cycle and sets SERR (PCI Status register,
bit 14) to 1. The assertion of SERR follows the address
phase by two clock cycles. The Am79C976 controller
will not assert DEVSEL for a PCI transaction that has
an address parity error when PERREN and SERREN
are set to 1. See Figure 88.
8/01/00
DEVSEL
FRAME
TRDY
STOP
IRDY
C/BE
CLK
PAR
AD
1
1st DATA
2
BE
PAR
3
4
DATA
BE
5
PAR
P R E L I M I N A R Y
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Am79C976
During the data phase of an I/O write, memory-mapped
I/O write, or configuration write command that selects
the Am79C976 controller as target, the device samples
the AD[31:0] and C/BE[3:0] lines for parity on the clock
edge, and data is transferred as indicated by the asser-
tion of IRDY and TRDY. PAR is sampled in the following
clock cycle. If a parity error is detected and reporting of
that error is enabled by setting PERREN (PCI Com-
mand register, bit 6) to 1, PERR is asserted one clock
later. The parity error will always set PERR (PCI Status
register, bit 15) to 1 even when PERREN is cleared to
0. The Am79C976 controller will finish a transaction
that has a data parity error in the normal way by assert-
ing TRDY. The corrupted data will be written to the
addressed location.
Figure 9 shows a transaction that suffered a parity error
at the time data was transferred (clock 7, IRDY and
TRDY are both asserted). PERR is driven high at the
beginning of the data phase and then drops low due to
the parity error on clock 9, two clock cycles after the
data was transferred. After PERR is driven low, the
Am79C976 controller drives PERR high for one clock
cycle, since PERR is a sustained tri-state signal.
DEVSEL
FRAME
SERR
C/BE
CLK
PAR
AD
1
2
ADDR
CMD
3
PAR
4
1st DATA
BE
PAR
5
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