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Chapter 4 - AT Commands, S-Registers, and Result Codes
&D4 Ignores DTR when answering a data call. If DTR is low when an
incoming data call is present, the TA will answer the call. If DTR
goes high during that call, nothing will happen. However, if DTR
goes high and then drops for the minimum time specified by S25,
then the call will be disconnected just as it would with &D1. &D4 is
the same as &D1, except that &D4 can answer a data call without
DTR and DTR can remain low for the duration of the call, but if DTR
goes high, then &D4 will behave like &D1.
Command: &En
Function: Flow Control
Values: n = 3–7, 12, 13
Default: &E4, &E6, &E13
Description:Selects method by which the TA controls the flow of data to and from the
computer to prevent either device from accepting data faster than it can
handle. The TA provides flow control in both directions. When the T A halts
data flow, it is called
flow control; when the computer halts data flow, it is
called
pacing.
&E3 Disable flow control by the TA
&E4 Hardware flow control. &E4 causes the TA to use the CTS signal on
pin 5 of the RS232E/V.24 interface to regulate flow control. When
CTS goes low, data flow from the computer is suspended until CTS
goes high again. This method works with pacing, which uses the
RTS signal on pin 4. Hardware flow control cannot be enabled
unless an error correction protocol is selected.
&E5 XON/XOFF flow control. This is an in-band method, in which the
XON and XOFF characters (^Q and ^S, respectively) are inserted
into the data stream, rather than using separate control lines. When
an XOFF character is detected, the data stream is suspended until
an XON character is detected. The drawback to this method is that
some files may contain these characters, causing the file transfer to
be suspended indefinitely.
&E6 When XON/XOFF pacing is active, TA responds to and discards the
XON/XOFF characters from the computer.
&E7 When XON/XOFF pacing is active, the TA responds to the XON/
XOFF characters and passes them through the communications link
to the remote device, thereby pacing the remote terminal adapter as
well.
&E12 Disables pacing
&E13 Enables pacing
Command: #Xn
Function: Send Single/Multiple Xoff Characters
Values: n = 0 or 1
Default: #X0
Description:Allows TA to send either a single or multiple Xoff characters to exert flow
control to the terminal.
The #X0 command (factory default setting) causes one Xoff to be sent until
the MTA128ST-USB's buffer reaches the Xon level. The #X1 command uses
an Xoff to be sent for every character received after TA reaches its buffer full
level.
#X0 One Xoff character sent until buffer reaches the Xon level (default)
#X1 Multiple Xoff characters sent for every character received after buffer
reaches the full level