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9.2 EXTENSIONS TO A AND C BIT HANDLING
The option bit, MAC_MODE_CTL, in control register B and the TR_BR_FWD input signal
give the MAC extended capabilities for handling the A and C bit fields at the end of
received frames (Table 9-1). These extensions are particularly useful for certain bridging
protocols.
When RABORT2 in control register B is a one, the ADDR16 output becomes an input,
RABORT2, with the same functionality as the RABORT input.
Inputs
Function
End Station
MLA/MSA/ EXT MATCH
Ar = R
Cr = x
Ar = S
Cr = x
EXT_DA_MATCH = 0
(Normal Match Mode)
Bridge Mode
Source Routing MATCH
Ar = R
Cr = x
Ar = S
Cr = x
EXT_DA_MATCH = 1
(Extended Match Mode)
Bridge Mode Promiscuous
Ar = x
Cr = x
EXT_DA_MATCH = 0
(Normal Match Mode)
Bridge Mode
Transparent_Bridge_Forward
Ar = R
Cr = x
Ar = S
Cr = x
EXT_DA_MATCH = 1
(Extended Match Mode)
NOTES:
1. Abort is RABORT (TX_RC_CONTROL control register B Bit 3 (ADR_RABR_CTL)=0)
Abort is RABORT (or RABORT2 if TX_RC_CONTROL control register B Bit 3 (ADR_RABR_CTL)=1)
2. S
= Set
R
= Reset
RPT = Repeat
x
= Don't care
3. MAC_MODE_CTL = RC_TX_CONTROL control register B Bit 2
EXT_ DA_MATCH = RC_TX_CONTROL control register B Bit 4
9- 4
Table 9-1. MAC A and C Bit Control
Ax
Always
Non-Abort
A
C
(Frame Copied)
S
S
S
S
S
S
S
S
RPT
RPT
S
RPT
RPT
Ar = A Received
Ax = A Transmitted
Cr = C Received
Cx = C Transmitted
MC68838 USER'S MANUAL
Outputs
Cx
Abort (see Note 1)
C
(MAC_MODE_CTL = 0,
Frame Flushed)
RPT
RPT
RPT
RPT
RPT
RPT
C
(MAC_MODE_CTL = 1,
Frame Flushed)
R
RPT
R
RPT
RPT
RPT
MOTOROLA
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