MAS3690CD datasheet(5/41 Pages) DYNEX

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MA3690/1/3

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Four bits of the Instruction word (bits 10-7) define

conditions under which the terminal will generate an interrupt

to the subsystem (IRQN). Note that the generation of IRQN will

only take place after any selected retry conditions have been

exhausted.

The interrupt conditions which may be selected can be

categorised as follows:

1. Interrupt if no response - the terminal will generate an

interrupt if the RT does not respond.

2. Interrupt if Status bit set - the terminal will generate an

interrupt if a received status word has a bit set other

than in the RT address field or if the wrong RT

responds.

3. Interrupt Always - the terminal will generate an

interrupt regardless of whether the message was

successful or not.

4. Interrupt if word error - the terminal will generate an

interrupt if a word encoding or word count error

occurs.

In all of the above cases, the terminal will generate a 250ns

pulse on IRQN and enter the halted state. This will occur after

the Report sequence has been executed.

Note the INCADRN will not be produced.

Retry Condition

Code

Definition

001

Retry if error

010

Retry if status bit set

100

Retry if busy set

Three bits of the Instruction word (bits 13-11) are used as

flags to specify conditions under which the terminal will

execute automatic message retries until the retry number

count is zero. The retry flags are involved with the following

conditions:

1. Retry if error - this includes a no-status response, a

word encoding error, or a wrong word count from a

responding RT.

2. Retry if Status bit set - an automatic retry will take

place if a received status word has a bit set, other

than in the RT address field, or if the wrong RT

responds.

3. Retry if Busy - this is a specific check for the setting of

the Busy bit in a responding RT’s status word.

The remaining two bits of the Instruction word specify the

number of message retries which the Bus Controller will

attempt automatically. A code of 00 specifies no retries, a code

of 11 specifies the maximum of three retries. The retries are in

addition to the initial message transmitted, hence a message

may be transmitted four times in total, if not successful. Note

that if the condition which is being tested becomes invalid, the

retry sequence will discontinue on the next message with the

Bus Controller completing execution of the message in the

relevant manner.

Retry Count

The two most significant bits of the instruction word specify

the number of retries to be carried out when a retry condition

has been detected. (Maximun 3 given by code 11)

RECEIVE COMMAND WORD

The receive command word is addressed when CODENN

and C1 are both low and R/WN and C0 are both high. This

word is the command word which will be transmitted for a BC

to RT transfer or as the first command word of an RT to RT

transfer.

Note: This word should be set to 1111 HEX if the message

code is 000 or 100, or if the Function Code is not 00.

TRANSMIT COMMAND WORD

The transmit command word is addressed when CODENN

and C0 are both low and R/WN and C1 are both high. This

word is the command word which will be transmitted for an RT

to BC transfer or as the second command word of an RT to RT

transfer.

Note: This word should be set to 1111 HEX if the message

code is 001 or 101, or if the Function Code is not 00.

DATA POINTER WORD

The data pointer word is addressed when CODENN is low

and C0, C1 and R/WN are all high. This word is intended as a

base address pointer to the subsystem data store thus

specifying where any data words associated with the current

instruction should be stored or retrieved from. As such, this

word is not read into the terminal itself but is merely transferred

from the Instruction Store to a suitable external address latch.

(The BUFENN signal is therefore inactive during this transfer).

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