MODEM CONTROL REGISTER
This register is located at I/O address [base+4], and is used to
control the interface with the modem or device used in place of a modem.
This register allows the states of the "modem control signals" to be
changed. These are DTR (Data Terminal Ready) and RTS (Request To
Send). It is also possible to place the UART in a loopback mode for
testing. Finally, the user-defined outputs OUT1 and OUT2 are controlled
from this register.
The DS-102 handles the OUT1 and OUT2 signals in the manner
appropriate for maintaining compatibility with standard PC serial ports:
|The OUT1 output is not connected.
|The OUT2 output is used to globally enable interrupts to
the computer. It should be active at all times if interrupts
are being used.
DTR --- Data terminal ready:
When this bit is set (logic 1), the DTR output is forced active to a logic 0.
When cleared (logic 0), the DTR output is forced inactive to a logic 1.
0
RTS --- Request to send:
When this bit is set (logic 1), the RTS output is forced active to a logic 0.
When cleared (logic 0), the RTS output is forced inactive to a logic 1.
1
OUT1 --- Output 1:
When this bit is set (logic 1), the OUT1 output is forced active to a logic 0.
When cleared (logic 0), the OUT1 output is forced inactive to a logic 1.
Not connected on the DS-102.
2
OUT2 --- Output 2:
When this bit is set (logic 1), the OUT2 output is forced active to a logic 0.
When cleared (logic 0), the OUT2 output is forced inactive to a logic 1.
Used for interrupt enable on the DS-102.
3
LOOP --- Loopback enable:
When set (logic 1), the transmitter shift register is connected directly to the
receiver shift register. The MODEM control inputs are internally connected
to the MODEM control outputs and the outputs are forced to the inactive
state. All characters transmitted are immediately received to verify
transmit and receive data paths. Transmitter and receiver interrupts still
operate normally. MODEM control interrupts are available but are now
controlled through the MODEM control register.
4
0 --- reserved
5
0 --- reserved
6
0 --- reserved
7
DESCRIPTION
BIT
Figure 21 --- Modem Control Register bit definitions
20
Quatech
DS-102 User's Manual