Modem Control Register (Mcr N ) - Intel 386 User Manual

Intel386™ EX EMBEDDED MICROPROCESSOR USER'S MANUAL
Modem Control
MCR0, MCR1
(read/write)
7
— —
Bit Bit
Number Mnemonic
7–5 —
4 LOOP
3–2 OUT2:1
1 RTS
0 DTR
11-30
— LOOP
Reserved; for compatibility with future devices, write zeros to these bits.
Loop Back Test Mode:
0 = Normal mode
1 = Setting this bit puts the SIO n into diagnostic (or loop back test) mode. This causes
the SIO channel to:
• set its transmit serial output (TXD n )
• disconnect its receive serial input (RXD n ) from the package pin
• loop back the transmitter shift register's output to the receive shift register's input
• disconnect the modem control inputs (CTS n #, DSR n #, RI n #, and DCD n #) from the
package pins
• force modem control outputs (RTS n # and DTR n #) to their inactive states
• connects MCR n bits to MSR n bits
Test Bits:
In diagnostic mode (bit 4=1), these bits control the ring indicator (RI n ) and data carrier
detect (DCD n# ) modem inputs. Setting OUT1 activates the internal RI n bit; clearing
OUT1 deactivates the internal RI n bit. Setting OUT2 activates the internal DCD n bit;
clear OUT2 deactivates the internal DCD n bit.
In normal user mode (bit 4=0) OUT1 has no effect and OUT2 in conjunction with
INTCFG.5/6 selects internal SIO interrupt or external interrupt. See Table 5-1 on page
5-8 for the configuration options.
Ready to Send:
The function of this bit depends on whether the SIO n is in diagnostic mode
(MCR n .4=1), internal connection mode, or standard mode.
In diagnostic mode, setting this bit activates the internal CTS n bit; clearing this bit
deactivates the internal CTS n bit.
In internal connection mode, setting this bit activates the internal CTS n # signal and the
RTS n # pin; clearing this bit deactivates the internal CTS n # signal and the RTS n # pin.
In standard mode, setting this bit activates the RTS n # pin; clearing this bit deactivates
the RTS n # pin. Note that pin is inverted from bit.
Data Terminal Ready:
The function of this bit depends on whether the SIO n is in diagnostic mode
(MCR n .4=1), internal connection mode, or standard mode.
In diagnostic mode, setting this bit activates the internal DSR n # signal; clearing this bit
deactivates the internal DSR n # signal.
In internal connection mode, setting this bit activates the internal DSR n # and DCD n #
signals and the DTR n # pin; clearing this bit deactivates the internal DSR n # and DCD n #
signals and the DTR n # pin. Note that pin is inverted from bit.
In standard mode, setting this bit activates the DTR n # pin; clearing this bit deactivates
the DTR n # pin. Note that pin is inverted from bit.
Figure 11-21. Modem Control Register (MCR n )
MCR0
Expanded Addr: F4FCH
ISA Addr: 03FCH
Reset State: 00H
OUT2 OUT1
Function
MCR1
F8FCH
02FCH
00H
0
RTS DTR