FUNCTIONAL DESCRIPTION
M O D E M C O N T R O L R E G I S T E R
+------+
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
+------+
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 i n t e r n a l l y 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 , t h e M O D E M c o n t r o l i n p u t s a r e
i n t e r n a l l y 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 n d t h e o u t p u t s a r e f o r c e d t o t h e i r
i n a c t i v e s t a t e . 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
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 c o n t r o l l e d t h r o u g h t h e M O D E M c o n t r o l
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
f u n c t i o n s o n t h e i r r e s p e c t i v e o u t p u t s . W h e n t h e s e
b i t s a r e s e t ( l o g i c 1 ) i n t h e r e g i s t e r , t h e
a s s o c i a t e d o u t p u t i s f o r c e d t o a l o g i c 0 . W h e n
cleared (logic 0), the output is forced to a logic1.
OUT2 - Output 2:
C o n t r o l s t h e O U T 2 o u t p u t a s d e s c r i b e d a b o v e .
Used for interrupt enable, see section VI.
OUT1 - Output 1:
C o n t r o l s t h e O U T 1 o u t p u t a s d e s c r i b e d a b o v e .
OUT1 is unused on the DS-202 / DS-302.
RTS - Request To Send:
Controls the RTS output as described above.
Used for output driver control, see section VII.
DTR - Data Terminal Ready:
Controls the DTR output as described above.
Used for output driver control, see section VII.
