FUNCTIONAL DESCRIPTION
I I I E . 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
+------+
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 d i r e c t l y 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 n a c t i v e s t a t e . A l l c h a r a c t e r s t r a n s m i t t e d a r e
i m m e d i a t e l y r e c e i v e d 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 t e r a n d r e c e i v e r
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 . 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 a v a i l a b l e b u t a r e n o w
controlled through 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
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:
Controls the OUT2 output as described above.
OUT1 - Output 1:
Controls the OUT1 output as described above.
RTS - Request To Send:
Controls the RTS output as described above.
DTR - Data Terminal Ready:
C o n t r o l s t h e D T R o u t p u t a s d e s c r i b e d a b o v e .
Used for transmitter enable (see section VIII).
