dp83261 National Semiconductor Corporation, dp83261 Datasheet - Page 92

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

TXPASS
TXRDY
RQRDY
RQSEND
TXACK
RQEOF
RQABT
RQFINAL
Symbol
7 0 Signal Descriptions
Handshake
The Handshake signals control the Request Interface handshaking process They are used for token capture and transmission
of PDUs
Pin
28
29
23
24
30
25
27
26
I O
O
O
0
I
I
I
I
I
Transmit Pass Indicates the absence of a Service Opportunity This could result from an unusable
request class waiting for a token timer expiration or MAC Reset TXPASS is always asserted between
service opportunities It is deasserted when TXRDY signal is asserted at the beginning of a Service
Opportunity
Transmit Ready Indicates that the Transmitter is ready for another frame For a non-immediate
request a usable token must be held in order to transmit frames TXRDY is asserted when
a) A usable token is being held or
b) An immediate request becomes serviceable or
c) After frame transmission if the current Service Opportunity is still usable for another frame
It is deasserted when the TXPASS or TXACK signal is asserted
Request Ready Indicates that the Transmitter should attempt to provide a Service Opportunity as
indicated by the RQRCLS(3 – 0) signals one cycle before RQRDY is asserted The Service Opportunity
will be maintained as long as possible If RQRDY is asserted within 6 byte times after TXRDY signal is
asserted the Transmitter will wait at least L Max plus one Void frame (4 16 ms or 4 80 ms) for
RQSEND to be asserted before releasing the token
Request Send Indicates that the Transmitter should send the next frame The MRD(7 – 0) signals
convey the FC byte when the RQSEND signal is asserted If RQSEND is asserted within 6 byte times
after the TXRDY signal is asserted the Transmitter will send the frame with a minimum length
preamble If RQSEND is not asserted within L Max plus one Void frame after RQRDY signal has been
asserted (4 16 ms or 4 60 ms) the token may become unusable (due to a timer expiration)
For Immediate transmissions from the Claim or Beacon State (when RQCLM or RQBCN is asserted)
RQSEND must be asserted no later than 8 byte times after TXRDY is asserted
RQSEND may only be asserted when TXRDY and RQRDY signals are asserted and RQFINAL is
deasserted RQSEND must be deasserted not later than one byte time after TXRDY is deasserted
Transmit Acknowledge Indicates that the Transmitter is ready for the next data byte TXACK is
asserted when the FC byte is accepted on MRD7 – 0 and remains asserted for each additional data
byte accepted It is deasserted one byte time after RQEOF ro RQABT is asserted The signal is also
deasserted when TXABORT or TXPASS is asserted
Request End of Frame Indicates that MRD7 – 0 conveys the last data byte when asserted Normally
this is the last byte of the INFO field of the frame (exceptions FCS transparency invalid frame length)
RQEOF causes TXACK to be deasserted and is ignored if TXACK is not asserted
Request Abort Indicates that the current frame should be aborted Normally this causes the
Transmitter to generate a Void Claim or Beacon frame RQABT causes TXACK to be deasserted and
will prevent TXACK assertion The BMAC will ignore RQABT if asserted with RQEOF
Request Final Indicates that the final frame of the request has been presented to the MAC Interface
When asserted the Issue Token Class (as opposed to the Capture Token Class) becomes the new
Token Class (TXCLASS) RQFINAL may only be asserted when RQRDY is asserted and RQSEND is
deasserted RQFINAL is ignored unless RQRDY has been asserted for at least one byte time and the
service parameters have been valid for at least three byte times RQFINAL must be deasserted not
later than two byte times after RQSEND is deasserted
(Continued)
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Description