dp83261 National Semiconductor Corporation, dp83261 Datasheet - Page 29

• Manufacturer Part Number: dp83261
• Description: Bmac Device Fddi Media Access Controller
• Manufacturer: National Semiconductor Corporation

Bit
D4
D5
D6
D7
6 0 Control Information
Option Register (Continued)
Symbol
IRPT
IFCS
EMIND
ITC
Inhibit Repeat When enabled
1 the Ring Engine cannot enter the Transmitter Repeat and Issue Token states This causes all received
2 Void frames are not transmitted during a service opportunity
3 Idle to Repeat transition is inhibited and all received tokens and MAC frames except Lower Claim and
When the ring is operational enabling this option causes the Reset actions to occur upon the completion of
the Service Opportunity if any When the ring is not operational Immediate Requests are serviced and
continue to completion
The Inhibit Repeat option can be used to scrub the ring for a period longer than the Ring Latency The option is
also useful in full duplex applications
Implementer FCS Enables use of the standard CRC as the FCS on Implementer frames (FC FF
enabled Implementer frames are treated like all other frames When Implementer frames are received with
bad FCS and Er
On Implementer frames the Standard does not mandate the setting of the E Indicator on the result of the FCS
check This allows Implementers to use alternate Frame Check Sequences aside from the standard 32-bit
CRC Implementers may also choose not to use any FCS in applications such as packet voice
If other stations in the ring are using Implementer frames with a non-standard FCS if used this option may
cause an interoperability problem
External Matching Indicators Enables the setting of the transmitted A Indicator (Ax) as an S symbol when
the EA pin is set Also enables the setting of the transmitted C Indicator (Cx) as an S symbol when the VCOPY
pin is set if the A Indicator is set as a result of an external match The Copied Not Copied Frame Counters are
also incremented as a result of external comparisons when this option is enabled
Inhibit Token Capture When enabled the Ring Engine is prohibited from transmitting any (more) frames
This option prohibits entry to the Transmit Void and Data states from the Idle state and causes exit from the
Data state after the current frame has been transmitted
When enabled it is still possible to perform Immediate transmissions from the transmitter Claim and Beacon
states but not from the Data state
This option can be used to temporarily block normal data service It can also be used in conjunction with the
Inhibit Recovery Required option to permit access via the Control Interface to the MAC Parameter RAM during
MAC operation
PDUs to be stripped and prevents tokens from being issued
My Beacon frames are ignored (Lower Claim and My Beacon frames may be ignored by setting
Option IRR)
e
R the E Indicator is transmitted as S and EICT is incremented
(Continued)
29
Description
e
10) When