164
Am79C971
P R E L I M I N A R Y
4-0
RES
Reserved locations. Written as
zeros, read as undefined.
BCR17: I/O Base Address Upper
Bit
Name
Description
31-16 RES
Reserved locations. Written as
zeros and read as undefined.
15-0
IOBASEU
Reserved
H_RESET, the value in this regis-
ter will be undefined. The settings
of this register will have no effect
on any Am79C971 controller
function. It is only included for
software compatibility with other
PCnet family devices.
locations.
After
Read/Write accessible always.
IOBASEU is not affected by
S_RESET or STOP.
BCR18: Burst and Bus Control Register
Note:
Note that bits 15-0 in this register are program-
mable through the EEPROM.
Bit
Name
Description
31-16 RES
Reserved locations. Written as
zeros and read as undefined.
15-12 ROMTMG
Expansion ROM Timing. The val-
ue of ROMTMG is used to tune
the timing for all EBDATA
(BCR30) accesses to SRAM/
Flash/EPROM as well as all Ex-
pansion ROM accesses to Flash/
EPROM.
ROMTMG, during read opera-
tions, defines the time from when
the Am79C971 controller drives
the lower 8 or 16 bits of the Ex-
pansion Bus Address bus to
when the Am79C971 controller
latches in the data on the 8 or 16
bits of the Expansion Bus Data
inputs. ROMTMG, during write
operations, defines the time from
when the Am79C971 controller
drives the lower 8 or 16 bits of the
Expansion Bus Data to when the
EBWE and EROMCS deassert.
The differences in the sizes of the
Expansion Bus Address and
Data busses is due to the differ-
ence in the access for SRAM ver-
sus Flash/EPROM.
The register value specifies the
time in number of clock cycles +1
according to Table 33.
Note
: Programming ROMTNG
with a value of 0 is not permitted.
The access time for the Expan-
sion ROM or the EDBATA
(BCR30) device (t
ACC
) during
read operations can be calculat-
ed by subtracting the clock to out-
put delay for the EBUA_EBA[7:0]
outputs (t
v_A_D
) and by subtract-
ing the input to clock setup time
for the EBD[7:0] inputs (t
s_D
)
from the time defined by ROMT-
MG:
t
ACC
= ROMTMG * CLK period
*CLK_FAC - (t
v_A_D
) - (t
s_D
)
The access time for the Expan-
sion ROM or for the EDBATA
(BCR30) device (t
ACC)
during
write operations can be calculat-
ed by subtracting the clock to out-
put delay for the EBUA EBA[7:0]
outputs
(t
v_A_D
) and by adding
the input to clock setup time for
SRAM/Flash/EPRO inputs (t
s_D
)
from the time defined by ROMT-
MG:
t
ACC
= ROMTMG * CLK period *
CLK_FAC - (t
v_A_D
) - (t
s_D
)
Table 32.
Network Port Configuration
Effect on the
10BASE-T Port
Half-Duplex
Full-Duplex
Full-Duplex
AUIFD (bit
1)
X
0
1
FDEN (bit
0)
0
1
1
Effect on the AUI
Port
Half-Duplex
Half-Duplex
Full-Duplex
Effect on the GPSI
Port
Half-Duplex
Full-Duplex
Full-Duplex
Effect On the MII Port (ASEL =
0, PORTSEL = MII)
Half-Duplex
Full-Duplex
Full-Duplex
Table 33.
ROMTNG Programming Values
ROMTMG (bits 15-12)
1h<=n <=Fh
No. of Expansion Bus Cycles
n+1