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AMD
TIR8: Transmit Control
This register is the Transmitter Control register.
Bit
Name
7
TXRES
6
TXFR
5
DMA_SEL
4
EN_TX_CRC
3
RATE_SW
2–1
TCRC[1:0]
0
TXS
94
P R E L I M I N A R Y
Reset Value
Description
0
Transmit Reset. When this bit is set to 1, the internal Transmit Re-
set signal is asserted. When this bit is set to 0, the internal Transmit
Reset signal is deasserted. The transmit FIFO is NOT reset
by TXRES.
0
Transmit FIFO Reset. When this bit is set to 1, the internal Transmit
FIFO Reset signal is asserted. When this bit is set to 0, the internal
Transmit FIFO Reset signal is deasserted.
0
DMA Select. When this bit is set to 1, the TXFIFO Not_Full signal is
routed to both of the 80188 DMA channels. When this bit is set to 0,
the TXFIFO Not_Full signal is routed to only DMA channel 1 of
the 80188.
0
Enable CRC-based Transmission. When this bit is set to 1, the in-
itiation of a transmission will commence when the logical AND of
the TXS bit (TIR8, bit 0) and the CRC32_GOOD output of the
CRC32 block becomes TRUE. Typically, the EN_TX_CRC bit and
the TXS bit are set together during a reception, such that if the re-
ception concludes with a correct CRC32 indication, then the trans-
mit state machine will automatically be started. When this bit is set
to 0, initiation of transmission will commence solely on the basis of
the setting of the TXS bit (TIR8, bit 0).
–
Rate Switch. When this bit is set to 1, the rate of data transmission
will automatically change immediately following the transmission of
the last bit of the PFL
Frame Delimiter, where PFL is defined in TCR3, bits [3:0}. Since
the PFL field of TCR3 is typically used to demark the PHY HEADER
from the MAC data (and hence, it is used to determine the starting
point for MAC CRC32 calculation), the rate switch will typically oc-
cur on the PHY/MAC boundary. The rate of transmission will
change from DR to DR XOR 0x1, where DR is the Data Rate field as
defined in TCR30, bits [2:0}. When this bit is set to 0, no rate switch
will occur. RX operations are unaffected by this bit. For rate switch-
ing on the RX side, an external decode to RX clock and TX data is
typically performed.
00b
Transmit CRC type. These two bits are used to determine the na-
ture of the CRC field that is appended to the current frame. These
bits must be stable throughout any given transmission. The follow-
ing interpretations have been assigned to these bits:
TCRC[1:0]
0
Transmit Start.
When this bit is set to 1, then the transmit state machine begins op-
eration. The transmit state machine is edge-sensitive; that is, this
bit must be reset to 0 and set again to 1 before a subsequent trans-
mission will begin. The transmit busy bit will be set in the transmit
status register (TIR9) to indicate the state of transmit. Resetting this
bit to 0 during transmission will not cause the current transmission
to be aborted. Transmission abort is performed with the TXRES bit.
Am79C930
th
byte that follows the last bit of the Start of
Transmitted CRC
00
No CRC is appended
01
CRC8 is appended
10
CRC32 is appended
11
No CRC is appended
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