am79c974 Advanced Micro Devices, am79c974 Datasheet - Page 62

• Manufacturer Part Number: am79c974
• Description: Pcnettm-scsi Combination Ethernet And Scsi Controller For Pci Systems
• Manufacturer: Advanced Micro Devices

APROM Access
The APROM space is a convenient place to store the
value of the 48-bit IEEE station address. This space is
automatically loaded from the serial EEPROM, if an
EEPROM is present. It can be overwritten by the host
computer. Its contents have no effect on the operation of
the controller. The software must copy the station ad-
dress from the APROM space to the initialization block
or to CSR12-14 in order for the receiver to accept
unicast frames directed to this station.
When programmed for WIO mode, any byte or word ad-
dress from an offset of 0h to an offset of Fh may be read.
An appropriate byte or word of APROM contents will be
delivered by the Am79C974 controller in response to ac-
cesses that fall within the APROM range of 0h to Fh.
When programmed for DWIO mode, only DWORD ad-
dresses from an offset of 0h to an offset of Fh may be
read. An appropriate DWORD of APROM contents will
be delivered in response to accesses that fall within the
APROM range of 0h to Fh.
Accesses of non-DWORD quantities are not allowed in
DWIO mode, even though such an access may be prop-
erly aligned to a DWORD address boundary.
Write access to any of the APROM locations is allowed,
but only 4 bytes on DWORD boundaries in DWIO mode
or 2 bytes on word boundaries in WIO mode (only read
accesses to the APROM locations can be in 8-bit quanti-
ties while in WIO mode). The IESRWE bit (see BCR2)
must be set in order to enable a write operation to the
APROM. Only the Am79C974 controller on-board IEEE
Shadow registers are modified by writes to APROM lo-
cations. The EEPROM is unaffected by writes to
APROM locations.
Note that the APROM locations occupy 16 bytes of
space, yet the IEEE station address requirement is for 6
bytes. The 6 bytes of IEEE station address occupy the
first 6 locations of the APROM space. The next six bytes
are reserved. Bytes 12 and 13 should match the value of
the checksum of bytes 1 through 11 and 14 and 15.
Bytes 14 and 15 should each be ASCII W (57h). The
above requirements must be met in order to be compat-
ible with AMD driver software.
RDP Access (CSR Register Space)
RDP = Register Data Port. The RDP is used with the
RAP to gain access to any of the Am79C974 controller
CSR locations.
Access to any of the CSR locations of the Am79C974
controller is performed through the Am79C974 control-
lers Register Data Port (RDP). In order to access a par-
ticular CSR location, the Register Address Port (RAP)
should first be written with the appropriate CSR ad-
dress. The RDP now points to the selected CSR. A read
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P R E L I M I N A R Y
Am79C974
of the RDP will yield the selected CSRs data. A write to
the RDP will write to the selected CSR.
When programmed for WIO mode, the RDP has a width
of 16 bits, hence, all CSR locations have 16 bits of width.
Note that when accessing RDP, the upper two bytes of
the data bus will be undefined since the byte masks will
not be active for those bytes.
If DWIO mode has been invoked, then the RDP has a
width of 32 bits, hence, all CSR locations have 32 bits of
width and the upper two bytes of the data bus will be ac-
tive, as indicated by the byte mask. In this case, note
that the upper 16 bits of all CSR locations (except
CSR88) are reserved and written as ZEROs and read as
undefined values. Therefore, during RDP write opera-
tions in DWIO mode, the upper 16 bits of all CSR loca-
tions should be written as ZEROs.
RAP Access
RAP = Register Address Port. The RAP is used with the
RDP and with the BDP to gain access to any of the CSR
and BCR register locations, respectively. The RAP con-
tains the address pointer that will be used by an access
to either the RDP or BDP. Therefore, it is necessary to
set the RAP value before accessing a specific CSR or
BCR location. Once the RAP has been written with a
value, the RAP value remains unchanged until another
RAP write occurs, or until an H_RESET or S_RESET
occurs. RAP is set to all ZEROs when an H_RESET or
S_RESET occurs. RAP is unaffected by the STOP bit.
When programmed for WIO mode, the RAP has a width
of 16 bits. Note that when accessing RAP, the upper two
bytes of the data bus will be undefined since the byte
masks will not be active for those bytes
When programmed for DWIO mode, the RAP has a
width of 32 bits. In DWIO mode, the upper 16 bits of the
RAP are reserved and written as ZEROs and read as
undefined. These bits should be written as ZEROs.
BDP Access (BCR Register Space)
BDP = Bus Configuration Register Data Port. The BDP
is used with the RAP to gain access to any of the
Am79C974 controller BCR locations.
Access to any of the BCR locations of the Am79C974
controller is performed through the Am79C974 control-
lers BCR Data Port (BDP ); in order to access a particu-
lar BCR location, the Register Address Port (RAP)
should first be written with the appropriate BCR ad-
dress. The BDP now points to the selected BCR.
A read of the BDP will yield the selected BCR s data. A
write to the BDP will write to the selected BCR.
When programmed for WIO mode, the BDP has a width
of 16 bits, hence, all BCR locations have 16 bits of width
in WIO mode. Note that when operating in WIO mode,