
2-4
SYM53C876/876E Data Manual
Functional Description
PCI Functional Description
* See the DMODE register.
** See the CTEST3 register
Interrupt Acknowledge Command
The SYM53C876 does not respond to this com-
mand as a slave and it never generates this com-
mand as a master.
Special Cycle Command
The SYM53C876 does not respond to this com-
mand as a slave and it never generates this com-
mand as a master.
I/O Read Command
The I/O Read command is used to read data from
an agent mapped in I/O address space. All 32
address bits are decoded.
I/O Write Command
The I/O Write command is used to write data to
an agent mapped in I/O address space. All 32
address bits are decoded.
Reserved Commands
The SYM53C876 does not respond to reserved
commands as a slave, and it never generates these
commands as a master.
Memory Read Command
The Memory Read command reads data from an
agent mapped in the Memory Address Space.
The target is free to do an anticipatory read for
this command only if it can guarantee that such a
read has no side effects.
Memory Write Command
The Memory Write command writes data to an
agent mapped in the Memory Address Space.
When the target returns “ready”, it assumes
responsibility for the coherency (which includes
ordering) of the subject data.
Configuration Read Command
The Configuration Read command reads the con-
figuration space of each agent. An agent is
selected during a configuration access when its
IDSEL signal is asserted and AD(1-0) are 00.
During the address phase of a configuration cycle,
AD(7-2) address one of the 64 dword registers
(where byte enables address of the bytes within
each dword) in the configuration space of each
device and AD(31-11) are logical don’t cares to
the selected agent. AD(10-8) indicate which
device of a multi-function agent is being
addressed.
Table 2-1: PCI Bus Commands and Encoding
Types
C_BE
(3-0)
Command Type
Supported
as Master
Supported
as Slave
0000
Interrupt Acknowl-
edge
Special Cycle
I/O Read
I/O Write
Reserved
Reserved
Memory Read
Memory Write
Reserved
Reserved
Configuration Read
Configuration Write
Memory Read Mul-
tiple
No
No
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
No
Yes
Yes
n/a
n/a
Yes
Yes
n/a
n/a
No
No
Yes*
No
Yes
Yes
n/a
n/a
Yes
Yes
n/a
n/a
Yes
Yes
Yes
(defaults
to 0110)
No
Yes
(defaults
to 0110)
Yes
(defaults
to 0111)
1101
1110
Dual Address Cycle
Memory Read Line
No
Yes*
1111
Memory Write and
Invalidate
Yes**