Silicon Laboratories SI2493/57/34/15/04, SI2494/39 manual Synchronous Access Mode Settings, AT\N0

AN93

Prior to sending the ATDT to establish a synchronous access mode connection, the following commands and registers require initialization: +MS, +ES, +ESA, +ITF, +IFC, U87, and U7A.

As an example, the closest equivalent to the Legacy Synchronous DCE Mode is the following initialization setting.

With either Synchronous Access Submode, once a connection has been established, payload data are multiplexed with command/indicator information by use of <EM> shielding. With <EM> shielding, either of the two bytes <0x19> or <0x99> (used to represent <EM>) precedes a special command or special indicator.

Synchronous access mode <EM> shielding is designed to support XON/XOFF handshaking. As such, the bytes 0x13 and 0x11 (XON/XOFF) are considered to be special characters in the same way the 0x19 and 0x99 bytes, used for <EM>, are special.

Since the payload data are multiplexed with <EM> shielded command/indicator and possibly XON/XOFF characters, Transparency <EM> codes are defined for the purpose of allowing the host software to send 0x13, 0x11, 0x19 and 0x99 bytes to/from the DCE. For example, if one <0x99> character needs to be sent as payload, the host software sends <EM><0x76> instead. For a complete list <EM> commands and statuses, see Table 86.

Table 85. Synchronous Access Mode Settings

AT\N0	Required to disable MNP,V.42
	and other protocols
AT+ES = 6,,8	Enable synchronous access
	mode on originate or answer
	Send Abort on underrun/over-
AT+ESA = 0,0,0,,1,0	run in Framed Submode.
	Enable CRC generation and
	checking.
AT+IFC = 2,2	CTS/RTS Flow Control
	Controls CTS Flow Control
AT+ITF = 0383,0128	Threshold. CTS off at 383
	bytes, CTS On at 128 bytes.
	Direct to Framed Sub-mode
AT:U87,050A	upon connection. DCE starts
	to transmit upon receipt of 10
	bytes from the DTE.

126 Rev. 1.3