Quatech RS-422/485, MPA-200/300 Communications Register, TM ST Llen Rlen Rcken Tcken Rxden Txden

9 COMMUNICATIONS REGISTER

The MPA-200 is equipped with an onboard communications register which gives the user options pertaining to the clocks and testing. The user can specify the source and type of clock to be transmitted or received. Test mode bits pertain only to the DTE versions and can be ignored if using a MPA-200 configured DCE.

The address of this register is Base+4. Table 14 and the descriptions that follow detail the communications register.

NOTE:

The Local Loopback Test and the Remote Loopback Test cannot be performed simultaneously. Thus, bits D5 and D4 of the communications register should not be simultaneously set (logic 1) .

Table 14 COMMUNICATIONS Register - Read/Write

D7	D6	D5	D4	D3	D2	D1	D0
TM ST	0	LLEN	RLEN	RCKEN	TCKEN	RXDEN	TXDEN

D7 -TEST MODE STATUS (DTE only, read only):

This bit can read the status of the Test Mode signal on a DTE, allowing the user to monitor this signal without generating any interrupts.

D6 - Reserved, always 0.

D5 -LOCAL LOOPBACK ENABLE (DTE only):

When set (logic 1), this bit allows the DTE to test the functioning of the DTE/DCE interface and the transmit and receive sections of the local DCE. When cleared (logic 0), no testing occurs.

D4 -REMOTE LOOPBACK ENABLE (DTE only):

When set (logic 1), this bit allows the DTE to test the transmission path up to and through the remote DCE to the DTE interface and the similar return transmission path. When cleared (logic 0), no testing occurs. If jumper J8 is in place the Remote Loopback is also used to control the Sync input of the Channel A data receiver. This is useful in situations where it is desired to receive unformatted serial data.

23 Quatech Inc., MPA-200/300 Manual