Specifications

Interface Specifics 53

The Lead In byte of an extended packet is an ASCII Control-V character (16h).

The host can check for either a 'U' or ^V as the Lead-in byte. If the byte is a 'U',

the host knows 9 bytes will follow. If the byte is a ^V, 10 bytes will follow.

As with the standard packet, the Checksum is calculated by summing the bytes

without regard to overflow. The Key byte is included in the sum.

Checksum byte = <AAh> + <Lead in byte> + <8 Data bytes> +

The Key byte is not used by factory default.

Software Handshaking

The controller recognizes the software flow control convention of XON/ XOFF

(ASCII "Control Q" and "Control S"). If the host sends a ^S character to the

controller, outside the context of a command packet, the controller will stop

sending data to the host. Upon receipt of a ^Q, the controller will once again be

enabled to send data to the host.

The controller can also send XOFF/XON characters to the host as a software

handshaking method. Upon receipt of a valid command, a ^S character may be

sent to the host. When the command is processed completely, a corresponding ^Q

is sent. This will allow devices which do not properly handle hardware

handshaking signals to use software flow control.

Software handshaking may be enabled or disabled with the Parameter command

(see page 95). It is disabled by factory default.

Hardware Handshaking

The controller supports hardware handshake signals typically implemented in EIA

RS-232 communications. If the handshaking signals are not connected, the

controller defaults to a transmit-enabled mode.

If the handshaking signals are connected, the following protocol should be used:

The signal DSR (Data Set Ready) is kept asserted by the controller. This signal

indicates to the host that a controller is present and powered on.

The signal DTR (Data Terminal Ready) tells the controller that the host is present.

The controller will only transmit if DTR is asserted by the host. Typically, the host

should keep DTR asserted.

When the controller receives a valid command, it de-asserts the handshaking signal

CTS (Clear To Send). The host should suppress further output until the controller