PSB 2115
PSF 2115
Functional Description
Semiconductor Group
51
11.97
If the IPAC is operating in the auto mode, the window size (= number of outstanding
unacknowledged frames) is limited to 1; therefore an acknowledgment is expected for
every I frame sent with an XIF command. The acknowledgment may be provided either
by a received S or I frame with corresponding receive sequence number (see
figure 14
).
If no acknowledgment is received within a certain time (programmable), the IPAC
requests an acknowledgment by sending an S frame with the poll bit set (P = 1) (RR or
RNR). If no response is received again, this process is repeated in total CNT times (retry
count, programmable via TIMR1 register).
The termination of the transmission operation may be indicated either with:
– XPR interrupt, if a positive acknowledgment has been received,
– XMR interrupt, if a negative acknowledgment has been received, i.e. the transmitted
message must be repeated (XMR = Transmit Message Repeat),
– TIN interrupt, if no acknowledgment has been received at all after CNT times the
expiration of the time period
t
1
(TIN = Timer INterrupt, XPR interrupt is issued
additionally).
Note: Prerequisite for sending I frames in the auto mode (XIF) is that the internal
operational mode of the timer has been selected in the MODED register
(TMD bit = 1).
The transparent transmission of frames (XTF command) is possible in all message
transfer modes. The successful termination of a transparent transmission is indicated by
the XPR interrupt.
A transmission may be aborted from the outside (E
≠
D) which has the effect that the
stop/go bit is set to 1, provided DIM1-0 (MODED register) are programmed
appropriately. An example of this is the occurrence of an S bus D-channel collision. If
this happens before the first FIFO pool has been completely transmitted and released,
the IPAC will retransmit the frame automatically as soon as transmission is enabled
again. Thus no
μ
P interaction is required.
On the other hand, if a transmission is inhibited by the Stop/Go bit after the first pool has
already been released (and XPR generated), the IPAC aborts the frame and requests
the processor to repeat the frame with an XMR interrupt.
In LT-T mode the Stop/Go bit can be output on pin AUX7 which may be used for test
purposes.