Meridian America Link/Customer Controlled Routing manual Straight RS-232 cable

274Chapter 11: Peripheral device cabling interface

¥using a null-modem cable A null-modem cable (a special cable, or a cable with an adapter) crosses certain RS-232 data signals so that a DTE-to-DTE or DCE-to-DCE connection behaves like a standard DCE-to-DTE connection. A null-modem cable is shown in Figure 80.

Note that null-modem cables and connectors are commonly used in asynchronous connections (to terminals or modems, for example) but cannot always be used in synchronous connections (to the Host or AML). In particular, DTE-to-DTE synchronous connections cannot normally be used because the DCE side supplies the clock signal, so that in a DTE-to-DTE connection, no clock signal would be available. Likewise, DCE-to-DCE connections may or may not work in synchronous mode because each side thinks it controls the clock signal. Also, the port hardware implementation may not allow a DTE-to-DCE crossover connection.

Figure 79

Straight RS-232 cable

		Pin				Pin
		1				1
		2		2
		3			3
DTE		4		4			DCE
		5			5
		6			6
		7				7
		8				8
		20	20
	15					15
	17					17

Note 1: Equipment at either end may require special configuration to look like DTE or DCE so that a straight cable can be used.

Note 2: Pins 15 and 17 are used for some configurations.

553-3202-210 Standard October 1998