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Motorola MC68838 User Manual page 75

Media access controller
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IMMED_MODE—Ignore RING_OPERATIONAL for This Frame
0 = Use the normal FDDI mode that requires RING_OPERATIONAL to be one
before a frame can be sent even if TOKEN_TYPE = 00.
1 = Ignore the value of RING_OPERATIONAL for the determination of whether or
not to send this frame. Normally, TOKEN_TYPE = 00 when IMMED_MODE = 1.
SEND_FIRST—Always Send This Frame First
0 = The transmitter treats the frame normally. The SEND_FIRST and SEND_LAST
bits can be used to implement the stream concept in the FDDI MA_DATA
request service primitive. They can also be used to send a fixed number of
packets per token access opportunity (e.g., when both bits are one).
1 = The transmitter always ensures that this frame is the first one sent with this
token capture. If the token was captured to send an earlier frame when a frame
with a SEND_FIRST was given to the MAC, the MAC will release the token and
wait to capture a later token to send this frame
BCN_FRAME—Only Send This Frame in Beacon State
This bit is ignored if the MAC is in the FDX states (i.e., the frame is sent regardless of
the value of this bit).
0 = The frame is only sent in the Tx_Data state (state T2).
1 = The frame is only sent in the Tx_Beacon state (state T5) and if the
FSl_BEACON bit in control register B is set. ln this state, only the
BCN_FRAME, APPEND_CRC, and EXTRA_FS bits in the packet request
header have any effect on this frame. See 3.1.2 Control Register B
for a description of the FSI_BEACON bit.
SEND_LAST—Release Token after This Frame Is Sent
0 = The transmitter treats the frame normally (see the previous description of
SEND_FIRST).
1 = The transmitter always releases the token after sending this frame, even if this
frame was the first one sent with its associated token.
APPEND_CRC—Generate CRC and Add an FCS Field to the Frame
This bit is still used in the FDX states.
0 = Since the MAC transmitter will not add an FCS field, the packet should already
contain an FCS field as its last four octets. Whether or not an FCS field is
added only depends on this bit and is not affected by the FC field transmitted
(i.e., the transmitter does not know whether or not this frame is a reserved-for-
implementor frame).
1 = The MAC transmitter calculates the CRC and appends it to the end of the frame
passed to it by the FSI in the FCS field.
MOTOROLA
MC68838 USER'S MANUAL
8-5

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