MAS3690CD datasheet(4/41 Pages) DYNEX

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MA3690/1/3

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OPERATION IN BUS CONTROL MODE

For this mode of operation the RT/BC pin must be held in

the logic zero state. On power up the PUC or RESET line must

be pulsed low for a minimum of 500ns causing the chip set to

initialise and assume the halted state with the HALTED output

low. To release the terminal from the halted state, the

subsystem must drive the HALTREQ line through a low to high

transition, at which time the HALTED line will go inactive.

When the HALTED line goes inactive,the terminal will

address a four word deep Instruction Store as shown below,

using the C0 and Cl outputs.

This first instruction after a Reset is a NOOP.

INSTRUCTION STORE

Word

Instruction

Receive Command

Transmit Command

Data Pointer

The instruction word specifies the operation which the

terminal is to carry out, and is formatted in the following way:

Instruction Word

Bit

15.14. 13.12.11.

10.9.8.7.

6.5.

4.3.

2.1.0.

Retry

Interrupt

Bus

Functlon Message

Count Condition Conditlon

Select Code

Code

The significance of the instruction word bits are as follows:

Message Code

Code

Transfer Type

000

RT to BC

001

BC to RT

010

RT to RT, data to BC subsystem

011

RT to RT, no data to BC subsystem

100

Broadcast RT to BC, non data mode commands only

101

Broadcast BC to RT

110

Broadcast RT to RT, data to BC subsystem

111

Broadcast RT to RT, no data to BC subsystem

Mode Codes without data are followed by a NOOP.

Function Code

Code

Terminal Function

Execute message code

Perform self test

Monitor bus

No operation (NOOP)

The Function Code (bits 4 and 3 of the Instruction Word)

specifies the required terminal mode of operation.

Execute - Code 00

With the Function code bits set to 00, the terminal will

execute the message as defined in the Message code bits

Self Test - Code 01

If the terminal has been selected to perform a Self Test

then the terminal transmitter output stages will be disabled and

the self test sequence entered. At the end of the Self Test the

transmitter stages will be re-enabled and a Report sequence

will be activated, in order to report on the success, or failure, of

the Self Test.

Passive Monitor - Code 10

If the Function code of the Instruction word is 10 the

terminal will disable the transmitter output stages, suspend

table execution and merely monitor the specified bus for valid

words.

No Operation - Code 11

The No Operation code provides a means of introducing

delay or a wait sequence into the table operation. In selecting

this code the terminal will be forced into the Report sequence

and provide either an increment signal (INCADRN) or an

interrupt (IRQN) if the Interrupt Always flag in the Instruction

word has been selected.

Bus Select

Code

Definition

Transmit on bus 0

Transmit on bus 1

Note: Bit 6 of the instruction word is tied low internally.

The required data bus on which transactions take place is

defined by bit 5. In addition to this, this bit defines the bus on

which the Transmitter Self Test operation will be conducted

and the choice of the bus for monitor purposes in Passive

Monitor mode.

Interrupt Condition

Code

Definition

0001

Interrupt if no response

0010

Interrupt if status bit set

0100

Interrupt always

1000

Interrupt if word error

If the terminal detects one of the above conditions and the

appropriate flag is set, the the IRQ line will pulse low for 250ns.

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