Texas Instruments 990 User Manual page 242

Communications Structures
The format of the receive ready packet is as follows:
BIT NUMBER
o
2
3 4 5 6 7
VIRTUAL
BYTE 0 0 0
0 1 CHANNEL
GROUP
LOGICAL CHANNEL NUMBER
2
P (R)
1
0
0 0 0 1
2280624
where:
Byte
a
is the general format identifier, 0001, followed by
the virtual channel group (VCG) number.
Byte 1 is the logical channel number (LCN). VCG and LCN
together form the logical channel identifier (LCI).
Byte 2 is the receive ready packet identifier.
D.3.5 Data Packet
The data packet header is appended only to user data sent on the
PVC; it is not appended to the control packets previously
described • . Data packets are sequentially numbered using the peS)
parameter -and carry an embedded acknowledgement of the last data
packet received, peR). peR) is the sequence number of the next
expected data packet. peR) and peS) counters are maintained for
each PVC.
A data packet can be transmi tted when the following condi tions
are satis fied:
*
The LCI is assigned and the PVC is in the data transfer
state.
*
An RNR has not been received, or if one has been
received, the RNR condition no longer exists.
*
The se'nd window is not full.
D-8
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