Revision 1.02 – June 27, 2006
S5935 – PCI Product
Data Book
Table 37. Add-On General Control/Status Register
Bit
Description
31:29 nvRAM/EPROM Access Control. This field provides a method for access to the optional, external non-volatile mem-
ory. Write operations are achieved by a sequence of byte operations involving these bits and the 8-bit field of bits 23
through 16. The sequence requires that the low-order address, high-order address, and then a data byte be loaded
in order. Bit 31 of this field acts as an enable/clock and ready for the access to the external memory. D31 must be
written to a 1 before an access can begin, and subsequent accesses must wait for bit D31 to become zero (ready).
D31
0
D30
X
D29
X
W/R
W
W
W
W
W
R
Inactive
1
0
0
Load low address byte
Load high address byte
Begin write
1
0
1
1
1
0
1
1
1
Begin read
0
X
X
Ready
1
X
X
R
Busy
Cautionary note: The non-volatile memory interface is also available for access by the PCI bus interface. Accesses
by both the Add-On and PCI bus to the nv memory are not directly supported by this component. Software must be
designed to prevent the simultaneous access of nv memory to prevent data corruption within the memory and pro-
vide for accurate data retrieval.
28
27
Transfer Count Enable. When set, transfer counts are used for Add-On initiated bus master transfers. When clear,
transfer counts are ignored.
Mailbox Flag Reset. Writing a 1 to this bit causes all mailbox status flags to become reset (EMPTY). It is not neces-
sary to write this bit as 0 because it is used internally to produce a reset pulse. Since reading of this bit will always
produce zeros, this bit is write only.
26
25
24
Add-On to PCI FIFO Status Reset. Writing a one to this bit causes the Outbound (Bus master writes) FIFO empty
flag to set indicating empty and the FIFO FULL flag to reset and the FIFO Four Plus words available flag to reset. It
is not necessary to write this bit as zero because it is used internally to produce a reset pulse. Since reading of this
bit would always produce zeros, this bit is write only.
PCI to Add-On FIFO Status Reset. Writing a 1 to this bit causes the Inbound (Bus master reads) FIFO empty flag to
set indicating empty and the FIFO FULL flag to reset and the FIFO Four Plus spaces flag to set. It is not necessary
to write this bit as 0 because it is used internally to produce a reset pulse. Since reading of this bit would always pro-
duce zeros, this bit is write only.
Reserved. Always zero.
23:16 Non-volatile memory address/data port. This 8-bit field is used in conjunction with bit 31, 30 and 29 of this register to
access the external non-volatile memory. The contents written are either low address, high address, or data as
defined by bits 30 and 29. This register will contain the external non-volatile memory data when the proper read
sequence for bits 31 through 29 is performed.
15:12 BIST condition code. This field is directly connected to the PCI configuration self test register. Bit 15 through 12
maps with the BIST register bits 3 through 0, respectively.
11:8
7
Reserved. Always zero.
Add-On to PCI Transfer Count Equal Zero (RO). This bit as a one signifies that the write transfer count is all zeros.
Only when Add-On initiated bus mastering is enabled.
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