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CMX625

 2001 Consumer Microcircuits Limited

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D/625/2

The CMX625 cannot initiate MON communication directly in a multi-slave application. Each slave

must monitor the MON channel for its unique address in the first byte before processing the following

command. Each slave can therefore only drive the DU MON channel when specifically requested to

by the master.

(iii) The ‘D’ channel consists of two bits providing 16kbps for carrying D channel user data. This channel

is not used by the CMX625.

(iv) The ‘Command/Indicate’ channels, labelled C/I0 and C/I1, provide real time status information

between devices connected via the IOM-2 bus. The C/I0 in channel 0 consists of 4 bits and the C/I1

in channel 1 is 6 bits wide. The C/I0 in channel 0 is not used.

The C/I1 channel is shared by all devices on the IOM-2 bus with no mechanism for determining and

resolving contention. If multiple slave devices are expected to drive the C/I1 channel then care must

be taken to allocate different bits to each device. An example of C/I1 channel usage would be 6 slave

devices each allocated one of the 6 C/I1 bits. When a slave requires attention it asserts its own bit,

which is detected by the master as a C/I1 value change (generating a processor interrupt). The

processor would then initiate MON1 communications with the appropriate slave and service its

request.

This is an example of one usage, but the C/I1 bits may be used for any real time

command/indicate purpose dependent on system design and number of slaves on the IOM-2 bus.

The C/I1 Channel Output Control Code is encoded as follows (bits 0, 1 and 2 of the IOM CONTROL

Register):

C/I1 Channel Output Control

Code (IOM Control Register,

Bits 2, 1 and 0)

C/I1 Channel Output Bit Content

0 0 0

C/I1 bits 5-0 = all logic ‘1’, i.e. C/I1 output disabled

0 0 1

Interrupt Request (logic ‘0’) on C/I1 bit 0 )

0 1 0

Interrupt Request (logic ‘0’) on C/I1 bit 1 )

0 1 1

Interrupt Request (logic ‘0’) on C/I1 bit 2 ) all other bits logic ‘1’

1 0 0

Interrupt Request (logic ‘0’) on C/I1 bit 3 )

1 0 1

Interrupt Request (logic ‘0’) on C/I1 bit 4 )

1 1 0

Interrupt Request (logic ‘0’) on C/I1 bit 5 )

1 1 1

Status Register bits 7-2 on C/I1 bits 5-0

Code ‘000’ is provided to disable drive of the C/I1 channel for use when multiple slaves have

completely utilised the C/I1 channel resource. The Interrupt Mask Register settings are ignored and

the C/I1 bits are set to logic ‘1’.

For codes ‘001’ to ‘110’ a logic ‘0’ (Interrupt Request) is driven onto the appropriate C/I1 bit when the

Status Register bits contain an unmasked logic ‘1’ (set by the Interrupt Mask Register). This allows

other devices to use the remaining C/I bits for their own purposes. The master device would use the

change of the appropriate C/I bit to initiate a Status Register read from the CMX625.

Code ‘111’ and an unmasked Status Register (INTERRUPT MASK bits 2 to 7 are set to ‘1’) allows the

most significant 6 bits of the Status Register to be driven onto the C/I1 channel directly for use when

the CMX625 is the only slave utilising the C/I channel. If any of the Status bits are masked, by setting

the equivalent bit in the mask register to ‘0’, then a logic ’0’ will be routed to the appropriate C/I1 bit

and will not change.