PSB 21381/2
PSB 21383/4
Interfaces
Data Sheet
55
2001-03-12
The MONITOR transfer protocol rules are summarized in the following section
A pair of MX and MR in the inactive state for two or more consecutive frames indicates
an idle state or an end of transmission.
A start of a transmission is initiated by the transmitter by setting the MXC bit to ’1’
enabling the internal MX control. The receiver acknowledges the received first byte by
setting the MR control bit to ’1’ enabling the internal MR control.
The internal MX,MR control indicates or acknowledges a new byte in the MON slot by
toggling MX,MR from the active to the inactive state for one frame.
Two frames with the MX-bit in the inactive state indicate the end of transmission.
Two frames with the MR-bit set to inactive indicate a receiver request for abort.
The transmitter can delay a transmission sequence by sending the same byte
continuously. In that case the MX-bit remains active in the IOM-2 frame following the
first byte occurrence.
Since a double last-look criterion is implemented the receiver is able to receive the
MON slot data at least twice (in two consecutive frames). The receiver acknowledge
the data after the reception of two identical bytes in two successive frames.
To control this handshake procedure a collision detection mechanism is implemented
in the transmitter. This is done by making a collision check per bit on the transmitted
MONITOR data and the MX bit.
Monitor data will be transmitted repeatedly until its reception is acknowledged or the
transmission time-out timer expires.
Two frames with the MX bit in the inactive state indicates the end of a message
(EOM).
Transmission and reception of monitor messages can be performed simultaneously.
This feature is used by the SCOUT to send back the response before the transmission
from the controller is completed (the SCOUT does not wait for EOM from the
controller). MONITOR control commands nevertheless are processed sequential that
means e.g. during a read on a register no further command is executed.
2.2.4.2
Error Treatment
In case the SCOUT does not detect identical monitor messages in two successive
frames, transmission is not aborted. Instead the SCOUT will wait until two identical bytes
are received in succession.
A transmission is aborted by the SCOUT if
an error in the MR handshaking occurs
a collision on the IOM bus of the MONITOR data or MX bit occurs
the transmission time-out timer expires
A reception is aborted by the SCOUT if
an error in the handshaking occurs or
an abort request from the opposite device occurs