Operating instructions

METTLER TOLEDO AT/MT/UMT Balances

CL for Programmers

This method has the quite undeserved reputation of being complicated and only suitable

for current loop connections. It owes its apparent complexity mainly to the sophisticated

procedure used to set up the handshake, and the rigid distinction between text characters,

termination characters, and code extensions (ESC sequences). In practice, however,

simplifications can usually be applied (e.g. it can be assumed that the termination character

is always a line feed). Since the CL handshake protocol offers advantages in many

applications – like the feature where complete messages can be requested from the balance

individually, or the absence of unwanted control characters when handshake is not

established – a few tips will be given here to facilitate working with this protocol.

Initialization

The balance attempts to establish handshake operation not only after it is switched on, but

also after every break in the data line (disconnecting and connecting the cable, receipt of

a break from the peripheral device, switching on the peripheral device), and also after

selecting the CL mode in the configuration register. About 200 ms after the electrical

connections have been established, your device will receive the SYN character (Synchronous

Idle, ASCII 22, Control-V). The procedure that follows now depends on whether you wish

simply to slow down the balance’s transmissions using handshake signals, or whether the

balance also should report its readiness to receive commands.

Device-controlled Balance Output

Send the character ACK (Acknowledge, ASCII 06, control-F) to the balance. It will then

respond with exactly one data block, if available. Each additional ACK authorizes the

balance to send another message. Do not send more than one ACK before receiving a data

string; the balance will not store them.