Operational description, Control commands – Maple Systems OIT Family (ASCII) User Manual

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Operational Description

The OIT Family Operator Interface Terminals can read from and write to internal memory reg-

isters. The OIT stores predefined messages that can be displayed on the OIT screen. In addi-

tion, the OIT stores predefined ASCII strings that can be sent to the ASCII host. The OIT

Family Operator Interface Terminals communicate with the ASCII host by receiving and re-

sponding to control commands (specially constructed ASCII strings). The control commands

sent by the ASCII host, modify or read the OIT’s internal memory registers or request that a

predefined screen be displayed. Some of the OIT’s internal memory registers are reserved for

special use: the Message Request Register (MRR), the Current Message Register (CMR), the

Status Bit coils, the Key coils, and the Status LED coils.

Control Commands

Control commands are multiple ASCII characters, starting with the ESC control character

and ending with a command terminator or line terminator. These commands allow the ASCII

host to request and send information to the OIT. Control commands are always sent by the

ASCII host to the OIT. The first letter after the ESC control character is the command letter.

The command letter determines what action will be performed by the OIT. Following is any

necessary or optional command data. The command data is always in ASCII format, mean-

ing that all data are ASCII printable characters. The following rules must be adhered to when

the ASCII host sends a control command:

•

Each control command must begin with the ESC control character. The OIT ignores any

command not initiated with the ESC control character.

•

Each control command must end with a command terminator or line terminator. The OIT

responds with a timeout error code to any control command that does not.

•

The ASCII host must wait for the OIT to respond to a control command before initiating

another control command.

Note: The OIT normally responds immediately to any control command that is correctly sent by

the ASCII host. However, a delay of up to 250 msec is possible. The delay is further

lengthened by the turnaround, and intercharacter delays programmed into the OIT.

OIT Family Operation Manual (ASCII)

1010-0088, REV02

OIT

OIT Reads

Message #

Message Request

Host Writes

Message #

OIT Writes

Message #

Current Message

Host Reads
Message #

OIT Reads

& Writes

Status Bit, Key &

Status LED Coils

Host Reads

& Writes

OIT Reads

& Writes

Data and Coil

Registers

Host Reads

& Writes

ASCII Host

OIT Sends ASCII String

Host Sends Control Command

OIT MEMORY

Figure 4 Interaction Between the OIT and ASCII Host