SAB 82525
SAB 82526
SAF 82525
SAF 82526
Transmission of Frames
The HSCX autonomously transmits S commands and S responses in the auto-mode. Either
transparent or I-frames can be transmitted by the user. The software timer has to be operated
in the internal timer mode to transmit I-frames. After the frame has been transmitted, the timer
is self-started, the XFIFO is inhibited, and the HSCX waits for the arrival of a positive
acknowledgement. This acknowledgement can be provided by means of an S- or I-frame.
If no positive acknowledgement is received during time t , the HSCX transmits an S command
1
(p = 1), which must be followed by an S response (f = 1). If the S response is omitted, the
process is performed n1 times before it is terminated.
Upon the arrival of an acknowledgement or after the completion of this poll procedure the
XFIFO is enabled and an interrupt is forwarded to the µC. Interrupts may be triggered by the
following:
– message has been acknowledged as positive (XPR interrupt)
– message must be repeated (XMR interrupt)
– response has not been received (TIN interrupt)
Upon arrival of an RNR frame, the software timer is started and the status of the opposite
station is polled periodically after expiration of t , until the status "receive ready" has been
1
detected. The user is informed accordingly via interrupt. If no response is received after n1
times an interrupt will be generated (TIN interrupt). As a result, the process will be terminated
as illustrated in figure 11.
Note: The internal timer mode should only be used in the auto-mode.
Transparent frames can be transmitted in all operating modes. After the transmission of a
transparent frame the XFIFO is immediately enabled, which is confirmed by interrupt (XPR).
In this case, time monitoring can be performed with the timer in the external timer mode.
Semiconductor Group
29
SIEMENS [ Siemens Semiconductor Group ]
