IBM DS-2000 warranty Functional Description Modem Control Register

FUNCTIONAL DESCRIPTION

E . MODEM CONTROL REGISTER

	+------		+
D7		0
	+------		+
D6		0
	+------		+
D5		0
	+------		+
D4		LOOP	-----	Loopback enable
	+------		+
D3		OUT2	-----	Output	2
	+------		+
D2		OUT1	-----	Output	1
	+------		+
D1		RTS	-----	Request	to send
	+------		+
D0		DTR	-----	Data terminal ready
	+------		+

Figure 11. MODEM control register bit definitions.

LOOP - Loopback Enable:

W h e n s e t ( l o g i c 1 ) , t h e t r a n s m i t t e r s h i f t r e g i s t e r i s c o n n e c t e d t o t h e r e c e i v e r s h i f t r e g i s t e r a n d t h e M O D E M c o n t r o l i n p u t s a r e c o n n e c t e d t o t h e M O D E M c o n t r o l o u t p u t s . A l l characters transmitted are immediately received t o v e r i f y t r a n s m i t a n d r e c e i v e d a t a p a t h s . T r a n s m i t a n d r e c e i v e i n t e r r u p t s s t i l l o p e r a t e n o r m a l l y b u t M O D E M c o n t r o l i n t e r r u p t s a r e n o w controlled by the MODEM control register.

B i t s O U T 2 , O U T 1 , R T S , a n d D T R p e r f o r m i d e n t i c a l functions on their respective outputs . When these bits are set (logic 1) in the register, the associated output is forced to a logic 0. When cleared (logic 0), the output is forced to logic 1.

OUT2 - Output 2:

Controls the OUT2 output as described above. Used for interrupt enable. See section VII.

OUT1 - Output 1:

Controls the OUT1 output as described above. Unused on DS-2000.

RTS - Request To Send:

Controls the RTS output as described above.

DTR - Data Terminal Ready:

Controls the DTR output as described above. Used for half-duplex control. See section IX.

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