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Intel
®
IXP42X Product Line of Network Processors and IXC1100 Control Plane Processor
September 2006 DM
Order Number: 252480-006US 365
Universal Asynchronous Receiver Transceiver (UART)—Intel
®
IXP42X product line and IXC1100
control plane processors
10.5.1.9 Modem Control Register
Register Name: MCR
Hex Offset Address: 0xC800 1010 Reset Hex Value: 0x00000000
Register
Description:
Modem Control Register
Access: See below.
31 543210
(Reserved)
LOOP
OUT2
OUT1
RTS
DTR
Register MCR
Bits Name Description
31:5 (Reserved)
4 LOOP
Loop back test mode: This bit provides a local Loop back feature for
diagnostic testing of the UART. When LOOP is set to logic 1, the following will
occur:
The transmitter serial output is set to a logic 1 state.
The receiver serial input is disconnected from the pin.
The output of the Transmitter Shift register is “looped back” into the receiver
shift register input.
The four modem-control inputs (CTS#, DSR#, DCD#, and RI#) are
disconnected from the pins and the modem control output pin RTS_N is forced
to its inactive state.
Note: Coming out of the loop-back test mode may result in unpredictable
activation of the delta bits (bits 3:0) in the Modem Status Register
(MSR). It is recommended that MSR is read once to clear the delta bits
in the MSR.
The lower four bits of the Modem Control Register are connected to the upper
four Modem Status Register bits:
• DTR = 1 forces DSR to a 1
• RTS = 1 forces CTS to a 1
• OUT1 = 1 forces RI to a 1
• OUT2= 1 forces DCD to a 1
0 = Normal UART operation
1 = Test mode UART operation
3OUT2
Interrupt Mask:
The OUT2 bit is used to mask the UART’s interrupt output to
the Interrupt Controller unit.
OUT2 = 0 UART interrupt masked
OUT2 = 1 UART interrupt not masked
When LOOP=1, this bit is not used as interrupt mask. The interrupt goes to the
processor without mask in loop-back mode.
2OUT1Test bit: This bit is used only in loop-back test mode. See (LOOP) Above.
1RTS
Request to Send: This bit controls the Request to Send (RTS_N) output pin.
0 = RTS_N pin is 1
1 = RTS_N pin is 0
0DTR
Data Terminal Ready:
0 = DTR# pin is 1
1 = DTR# pin is 0