F U N C T I O N A L D E S C R I P T I O N
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 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
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 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
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
bits are set (logic 1) in the register, the associated
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 c l e a r e d ( l o g i c
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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