Chapter 3 - AT Commands

3.12 Flow Control Commands

Flow control refers to the techniques used by data terminal equipment and the modem to pause and resume the flow of information between them. It prevents a device from accepting more data than it can handle. The modem implements flow control in both directions. When the modem halts the flow of data, it is called flow control, and when the computer halts the flow, it is called pacing.

&BSn

Maximum Reliable Block Size

 

n = 0 or 1

 

Default: &BS1

 

When the modem is in reliable mode, use the &BS command to set the maximum size of a

 

data block. MNP Class 3 sends a 64-character block, while Classes 4 and 5 normally send

 

blocks of 256 characters or less. Reducing the block size for MNP 4 and 5 may improve

 

overall throughput whenphone lines are noisy; however, it also could slow data transfer if

 

line quality is good.

 

&BS0 sets the maximum transmit block size to 64 characters.

 

&BS1 sets the maximum transmit block size to 256 characters.

$EBn

Asynchronous Word Length

 

n = 0 or 1

 

Default: $EB0

 

The MT2834MR6 can operate with either a 10-bit format (one start bit, seven data bits, one

 

parity bit, and one stop bit) or an 11-bit format (one start bit, eight data bits, one parity bit,

 

and one stop bit) in both command and online modes.

 

$EB0 enables a 10-bit format It automatically detects parity when an AT command is

 

issued.

 

$EB1 enables an 11-bit format.

&E3

Flow Control Disable

 

The &E3 command completely disables data flow control initiated by the modem.

&E4

Hardware Flow Control

 

Factory default. The &E4 command enables the modem’s use of the Clear to Send (CTS)

 

signal on the RS-232/V.24 interface to regulate data flow. When CTS drops, data flow is

 

suspended until the signal goes high again. This method of flow control works in

 

conjunction with pacing (i.e., computer-initiated flow control), which uses the Request to

 

Send (RTS) signal on the RS-232/V.24 interface. Hardware flow control cannot be enabled

 

unless an active error correction protocol is selected.

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Multi-Tech Systems MT2834MR6 manual Flow Control Commands, BSn Maximum Reliable Block Size = 0 or Default &BS1