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Control Register B (Mac_Cntrl_B) - Motorola MC68838 User Manual

Media access controller
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lines (TPATHx and TPRITY) will affect the BIST. SYMCLK, RCDATx, and
TXCTLx have no effect during BIST.
RXPARITY—Generate Odd or Even Receive Parity
0 = The MAC generates RPRITY so that RPRITY and RPATHx have odd parity.
1 = The MAC generates RPRITY so that RPRITY and RPATHx have even parity.
NTE_AL_FRMS—Note All Frames
0 = The MAC sets the FRAME_RCVD bit in the interrupt event register only when the
frame count register overflows (i.e., potentially notifies the NP for every 65536
frames). lt is possible, though unlikely, for the DOUBLE_OVF bit not to be set
when FRAME_CT overflows. Therefore, NTE_AL_FRMS should not be set
unless the NP can read the FRAME_CT before it can overflow or unless precise
frame counts are not required.
1 = The MAC sets the FRAME_RCVD bit in the interrupt event register when the
FRAME_CT is incremented.

3.2.2 Control Register B (MAC_CNTRL_B)

Control register B controls the MAC transmitter. The NP can read and write this register at
any time. The MAC chip only modifies the RESET_FIELD bits. The register is cleared on
power-up reset and is unaffected by a MAC_Reset.
15
14
RING_PURGE
FDX_MODE
7
6
FSI_BEACON
DELAY_TOKEN
RING_PURGE—Enable Ring Purging Mode
This bit is ignored by the MAC when RING_OPERATIONAL is low or cleared or when
the chip is in the FDX states. Unlike BRIDGE_STRIP, RING_PURGE does not affect
frames the MAC thinks it sent and hence packets the MAC asks the FSI to flush (not
copy). Consequently, it is useful to set both BRIDGE_STRIP and RING_PURGE.
There is typically only one purging station per ring. The choice of the ring purger, if any,
is beyond the scope of the FDDI standard.
0 = The MAC operates normally.
1 = The MAC purges the ring upon every token rotation until the NP resets this bit.
The MAC performs the following operations:
Captures every token (unless RING_OPERATIONAL is zero),
Sends any FSI frames for which the token is usable,
Sends two special void frames (see the BRIDGE_STRIP bit description), and
Releases the token.
3- 8
13
12
BRIDGE_STRIP
TXPARITY_ON
5
4
IGNORE_
EXT_DA_
SACAM
MATCH
MC68838 USER'S MANUAL
11
10
REPEAT_ONLY
LOSE_CLAIM
3
2
RABORT2
MAC_MODE_
CTL
9
8
RESET_FIELD
1
0
0
0
MOTOROLA

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