Maple Systems OIT Family (ASCII) User Manual

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host and how the OIT notifies the ASCII host of OIT register updates. Regardless of the operating

mode, the OIT always immediately responds to control commands sent by the ASCII host.

Interactive Mode

In Interactive mode, the OIT immediately sends data to the host. For example, if a function key

is configured to send an ASCII string to the ASCII host, it will do so whenever it is pressed. If a

read/write register monitor is displayed on the OIT and the OIT operator changes the value, the

new value is immediately sent to the ASCII host when the Enter key is pressed (provided that

the “Notify Host of Read/Write Register Monitor Update” feature is enabled).

Each control command sent by the ASCII host is immediately processed by the OIT and a re-

sponse sent back. The control command must be in the correct format and must include either

a command terminator or a line terminator or both. The OIT responds with an error code, the

data that the host controller requested, and the programmed line terminator.

Network Mode

The ASCII Slave protocol provides networking of up to 100 OITs. To communicate with a

particular OIT terminal, the ASCII host sends that OIT’s network address (1 to 100) as two

ASCII hexadecimal characters. This is called “logging on” to the OIT. The ASCII host can

then send control commands to the OIT, the same as in Interactive mode. The ASCII host

must send a line terminator to close communications with the OIT. The line terminator alerts

all OITs on the network that a new communication session is about to begin and that the next

two characters sent will be an OIT’s network address.

When the ASCII host communicates to a single OIT, the OIT with the correct network address

responds to the control command as it would in Interactive mode. The ASCII host can send an

identical message to all of the OITs on the network by using the global broadcast address of

“00”. The OITs do not return a response to the host when the global address is used; this pre-

vents the OITs from corrupting each other’s messages by trying to talk at the same time.

When using a global broadcast, the ASCII host must send a line terminator to “log off” all of

the OITs on the network before beginning a session with one particular OIT.

As stated above, the line terminator is used to “log off” communications with one OIT and

start talking to another OIT. If the line terminator is not sent after a control command is sent,

the command terminator must be sent instead. If the command terminator is sent, then the

host remains “logged on” to the OIT. In this fashion, any future control command sent to the

OIT does not have to carry the OIT address designator.

In Network mode, the OIT immediately responds to control commands sent from the ASCII

host. If the OIT operator performs input which is to be sent to the ASCII host (such as pressing

a function key that is configured to send an ASCII string, or changing a value in a register mon-

itor when the “Notify Host of Read/Write Register Monitor Updates” feature is enabled) then

this input is stored in an internal polling buffer. The buffer stores up to 200 characters (includ-

ing the line terminator). If the OIT is not polled by the ASCII host before the buffer becomes

full, any additional operator input that is meant to be sent to the ASCII host is lost.

When configuring the OITs for network mode, all of them must use the same line terminator.

Note: In Network mode, the line terminator also acts as a command terminator. This means

that any

STX ETX

combinations from the ASCII host can be shortened to

ETX

OPERATION

1010-0088, REV02