Northern UTA220/UTA220k manual Parameter 5 Ancillary Device Control

D-Channel X.25

Parameter 5: Ancillary Device Control

Parameter 5 specifies whether or not flow control of the local DTE device (ancillary device) by the PAD can occur, and if so, what modes of the PAD the PAD flow control of the local DTE are allowed. Flow control of the local DTE device is handled in conjunction with S54 (DTE flow control register). The type of flow control the PAD transmits to the local DTE device is set according to the setting of S54. For example, if S54 is set for CTS flow control, the PAD will flow control the local DTE device by turning off the CTS pin when the PAD can no longer accept any characters from the local DTE. When the PAD can resume accepting characters from the local DTE, the PAD turns the CTS pin on. If all the DTE flow control options are disabled (default), the PAD will transmit XON (Ctrl Q) and XOFF (Ctrl S) to the local DTE for flow control.

Table 12-11: Ancillary Device Control

Value Description

0No PAD flow control

1PAD data transfer flow control

2PAD data transfer and PAD command mode flow control *

*default

Note: The function of parameter 5 differs from the 1984 CCITT X.3 Specification. The specification indicates that only XON and XOFF can be transmitted to the DTE for the purpose of flow control. The TA does not restrict the type of flow control used on the local DTE. The setting of the AT command indicates the type of flow control sent to the DTE. Thus, if the DTE device only recognizes CTS flow control, the PAD can still flow control the DTE.

Parameter 6: Control of PAD Service Signals

Parameter 6 specifies whether the PAD prompt or PAD service signals are transmitted to the local DTE device by the PAD, and the format of those service signals. The PAD service signals are character messages transmitted to the local DTE device by the PAD in response to PAD commands issued by the local DTE or to inform the user of a packet or network action (i.e., call reset etc.). The PAD prompt is the character *. It is transmitted by the PAD to the local DTE device when the PAD is in PAD command mode to prompt the user to enter a PAD command.

For non-interactive applications, the service signal transmission to the local DTE may be disabled as the transmission service signals can appear to be part of the received data.

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