ISDN TA POTS Interface

CMX625

 2001 Consumer Microcircuits Limited

12

D/625/2

Figure 6 shows the monitor channel handshake procedure.

MX = Monitor Transmit Bit, active low.

MR = Monitor Receive Bit, active high.

MD = Monitor Data

Figure 6 Monitor Channel Handshake Procedure

Figure 7 shows the maximum speed case for monitor handshake timing. The transmitter can be designed

for a higher data throughput than is provided by the general case. The transmitter can deactivate (high)

MX and transmit new data one frame after MR is deactivated. In this way, the transmitter is anticipating

that MR will be reactivated one frame after it is deactivated, minimising the delay between bytes. MR

being held inactive (high) for two or more frames indicates an abort is being signalled by the receiver.

Byte 1

Byte 2

Byte 3

Byte n

ACK

ACK

ACK

ACK

EOM

MR

MX

Data

Figure 7 Monitor Handshake Timing (maximum speed case)

The abort is a signal from the receiver to the transmitter indicating that data has been missed. The

receiver is able to abort a transmission by holding MR inactive (high) for two or more frames in response

to MX going active. An abort from the receiver will generate an interrupt when the INTERRUPT MASK

Register bit 2 is unmasked (logic ‘1’) and bit 2 of the Status Register will be set to ‘1’. Figure 8 shows a

monitor abort request from the receiver.