CRD8900-1 View Datasheet(PDF) - Cirrus Logic
Part Name
Description
MFG CO.
'CRD8900-1' PDF : 132 Pages View PDF
4.5 Initiate Transmit Registers
CS8900
Initiate Transmit Register
Transmit Command Request - TxCMD (Write-only)
F
E
D
C
B
A
TxPadDis InhibitCRC
9
Onecoll
Address: PacketPage base + 0144h
8
7
6
5-0
Force
TxStart
001001
The word written to PacketPage base + 0144h tells the CS8900 how the next packet should be transmitted. This
PacketPage location is write-only, and the written word can be read from Register 9, at PacketPage base +
0108h. The CS8900 does not transmit a frame if TxLength (at PacketPage location base + 0146h) is less than 3.
See Section 5.7.
BIT NAME
5-0 001001
7, 6 TxStart
8
Force
9
Onecoll
C InhibitCRC
D TxPadDis
DESCRIPTION
These bits provide an internal address used by the CS8900 to identify this as the
Transmit Command Register. When reading this register, these bits will be 001001,
where the LSB corresponds to Bit 0.
This pair of bits determines how many bytes are transferred to the CS8900 before the
MAC starts the packet transmit process.
Bit 7 Bit 6
0 0 Start transmission after 5 bytes are in the CS8900
0 1 Start transmission after 381 bytes are in the CS8900
1 0 Start transmission after 1021 bytes are in the CS8900
1 1 Start transmission after the entire frame is in the CS8900
When set in conjunction with a new transmit command, any transmit frames waiting in
the transmit buffer are deleted. If a previous packet has started transmission, that
packet is terminated within 64 bit times with a bad CRC.
When this bit is set, any transmission will be terminated after only one collision. When
clear, the CS8900 allows up to 16 normal collisions before terminating the transmission.
When set, the CRC is not appended to the transmission.
When TxPadDis is clear, if the host gives a transmit length less than 60 bytes and
InhibitCRC is set, then the CS8900 pads to 60 bytes. If the host gives a transmit length
less than 60 bytes and InhibitCRC is clear, then the CS8900 pads to 60 bytes and
appends the CRC.
When TxPadDis is set, the CS8900 allows the transmission of runt frames (a frame less
than 64 bytes). If InhibitCRC is clear, the CS8900 appends the CRC. If InhibitCRC is
set, the CS8900 does not append the CRC.
Since this register is write-only, it’s initial state after reset is undefined.
68
DS150PP2
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