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P R E L I M I N A R Y
AMD
97Am79C930
TIR12: Byte Count Register LSB
This register is the Byte count register LSB. This register
contains the lower 8 bits of the 12-bit byte count for
receive and transmit messages. This is a working
register; access by software is not needed for
normal operation.
Bit Name Reset Value Description
7:0 BC[7:0] 00h Byte Count. Lower eight bits of current byte count for both transmit
and receive operations. During transmit operations, the byte count
reflects the number of bytes that have been transmitted following
the transmission of the Start of Frame Delimiter. CRC is not in-
cluded in this count for TX. During receive operations, the byte
count reflects the number of bytes that have been written into the
RX FIFO. This total excludes Preamble and Start Of Frame
Delimiter bytes, but includes any PHY field and CRC bytes.
Write accesses to this register from the software will cause
unexpected results.
TIR13: Byte Count Register MSB
This register is the Byte count register MSB. This regis-
ter contains the upper 4 bits of the 12-bit byte count for
receive and transmit messages. This is a working
register; access by software is not needed for
normal operation.
Bit Name Reset Value Description
7–4 Reserved – Reserved. Must be written as a 0. Reads of this bit produce
undefined data.
3–0 BC[11:8] 0h Byte Count. Upper 4 bits of current byte count for both transmit and
receive operations. During transmit operations, the byte count re-
flects the number of bytes that have been transmitted following the
transmission of the Start of Frame Delimiter. CRC is not included in
this count for TX. During receive operations, the byte count reflects
the number of bytes that have been written into the RX FIFO. This
total excludes Preamble and Start Of Frame Delimiter bytes, but in-
cludes any PHY field and CRC bytes. Write accesses to this regis-
ter from the software will cause unexpected results.
TIR14: Byte Count Limit LSB
This register is the Byte Count Limit LSB register.
Bit Name Reset Value Description
7–0 BCLT[7:0] 00h Byte Count Limit. Lower eight bits of byte count limit for both trans-
mit and receive operations, depending upon which operation is
currently occurring. During transmit operations, when the byte
count limit is reached, an interrupt to the 80188 controller will be
generated if the TXBCNT interrupt has been unmasked. During TX,
the byte counter counts all bytes beginning with the first byte after
the SFD field has been detected and does not count the CRC bytes
appended to the TX frame. During RX, when the byte count limit is
reached, an interrupt to the 80188 controller will be generated if the
RXBCNT interrupt has been unmasked. During RX, the byte
counter counts all bytes that follow the Start of Frame Delimiter.
Byte count limit has no effect on state machine or
FIFO operations.