Intel PXA26X User Manual Page 384

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10-18 Intel® PXA26x Processor Family Developer’s Manual
Universal Asynchronous Receiver/Transmitter
Table 10-14. Modem Control Register MCR (Sheet 1 of 2)
Base+0x10 Modem Control Register UART
Bit
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Reserved
LOOP
OUT2
OUT1
RTS
DTR
Reset 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Read/Write
Bits Name Description
31:5 Reserved
4 LOOP
LOOPBACK MODE:
This bit provides a local loopback feature for diagnostic testing of the UART. When LOOP
is set to a 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 (nCTS, nDSR, nDCD, and nRI) are disconnected from the pins and the modem
control output pins (nRTS and nDTR) are forced to their inactive state.
Coming out of the loopback mode may result in unpredictable activation of the delta bits
(bits 3:0) in the Modem Status Register. It is recommended that MSR is read once to clear
the delta bits in the MSR.
Loopback mode must be configured before the UART is enabled.
The lower four bits of the MCR 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
In loopback mode, data that is transmitted is immediately received. This feature allows the
processor to verify the transmit and receive data paths of the UART. The transmit, receive
and modem control interrupts are operational, except the modem control interrupts are
activated by MCR bits, not the modem control pins. A break signal can also be transferred
from the transmitter section to the receiver section in loopback mode.
0 – Normal UART operation
1 – Loopback mode UART operation
3OUT2
OUT2 SIGNAL CONTROL:
OUT2 connects the UART’s interrupt output to the Interrupt Controller unit. When LOOP=0:
0 – UART interrupt is disabled.
1 – UART interrupt is enabled.
When LOOP=1, interrupts always go to the processor:
0 – MSR[DCD] forced to a 0
1 – MSR[DCD] forced to a 1
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