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8.3 PACKET REQUEST HEADER
The packet request header contains the control bytes presented to the MAC by the FSI.
This information is contained in three bytes that control the MAC transmitter process. The
third byte is currently ignored and should be passed as all zeros.
First Byte
7
6
FORMAT_TYPE
Second Byte
7
6
0
SEND_LAST
Third Byte
7
6
0
0
FORMAT_TYPE—Type of Packet Request Header
This field provides future MACs the ability to handle different packet request header
formats; should always be 00.
TOKEN_TYPE—Type of Token Required To Send This Frame
This field determines whether a restricted token, an unrestricted token, any token, or
no token is required to send this frame.
00 = Immediate mode. Transmission begins once the MAC enters the Tx_Idle state if
the REPEAT_ONLY bit is zero, if another recovery, reset, or token received
transition does not occur, and if RING_OPERATIONAL or immediate mode is
one. Even though a frame was transmitted without a token, the TOKEN_SEND
field could cause a token to be sent; normally, TOKEN_SEND is 00 (no token
sent).
1x = An unrestricted token can be used to send this frame.
x1 = A restricted token can be used to send this frame.
11 = Either type of token can be used to send this frame.
SYNCH_FRAME—Send Synchronous Frame
0 = Send this frame according to the rules for asynchronous frame transmission.
The corresponding bit in the FC field is ignored because the MAC does not
examine the FC field.
1 = Send this frame according to the rules for synchronous frame transmission.
8-4
5
4
TOKEN_TYPE
5
4
APPEND_CRC
TOKEN_SEND
5
4
0
0
MC68838 USER'S MANUAL
3
2
SYNCH_FRAM
IMMED_MODE
E
3
2
3
2
0
0
1
0
SEND_FIRST
BCN_FRAME
1
0
EXTRA_FS
1
0
0
0
MOTOROLA
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