MAS3690FD datasheet(9/41 Pages) DYNEX

9 / 41 page

MA3690/1/3

9/41

PASSIVE MONITOR

The terminal may be configured into a Passive Monitor (or

Bus Monitor) merely by selecting the appropriate Function

Code of the Instruction word. By doing this the terminal will not

take part in any further Instruction execution but instead will

monitor the selected bus for data transmissions.

INTERRUPT / RETRY CAPABILITY

The terminal has certain in-built functions which permit the

terminal to retrieve situations which would normally cause a

greater degree of subsystem intervention. This is achieved by

having an automatic retry facility in-built to the terminal which

is selectable from the Instruction word. In this case both the

condition and number of attempts for which the terminal must

try may be specified. After completion of the required number

of attempts, terminal operation may be halted with the

possibility of an interrupt generated also.

The interrupt facility provides a means of more direct

subsystem interaction in the event of a failure. Similar flags are

required to be set in the Instruction word before a selectable

interrupt may be generated. This form of interrupt also includes

an Interrupt Always flag whose application may be used to

determine subsystem/system timing requirements.

It should be noted that an interrupt may also be generated

by the error checking procedures of the terminal which verify

aspects of the Instruction word and associated Receive/

Transmit command words.

STANDBY BUS CONTROLLER

The terminal provides a number of signals to the

subsystem for message addressing and execution. Two

address lines are provided (CO, Cl) plus a signal to increment

an external counter (INCADRN). This, together with the on-

chip sequencing, error checking, etc., enables a standby bus

controller, using a fixed table of messages, to be realised in

few devices as shown in Figure 2. It is therefore possible to

attain a standby BC on a single 6 x 4 PCB card.

Figure 2: Standby Bus Controller

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