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3.7 Modem Control Register (MCR)
The modem control register (MCR) is shown in Figure 15 and described in Table 16. The modem control
register provides the ability to enable/disable the autoflow functions, and enable/disable the loopback
function for diagnostic purposes.
Figure 15. Modem Control Register (MCR)
31 16
Reserved
R-0
15 6 5 4 3 2 1 0
Reserved AFE
(1)
LOOP Reserved RTS
(1)
Rsvd
R-0 R/W-0 R/W-0 R-0 R/W-0 R-0
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
(1)
All UARTs do not support this feature, see the device-specific data manual for supported features. If this feature is not available, this bit
is reserved and should be cleared to 0.
Table 16. Modem Control Register (MCR) Field Descriptions
Bit Field Value Description
31-6 Reserved 0 Reserved
5 AFE Autoflow control enable. Autoflow control allows the RTS and CTS signals to provide handshaking
between UARTs during data transfer. When AFE = 1, the RTS bit determines the autoflow control
enabled. Note that all UARTs do not support this feature, see the device-specific data manual for
supported features. If this feature is not available, this bit is reserved and should be cleared to 0.
0 Autoflow control is disabled.
1 Autoflow control is enabled:
• When RTS = 0, CTS is only enabled.
• When RTS = 1, RTS and CTS are enabled.
4 LOOP Loop back mode enable. LOOP is used for the diagnostic testing using the loop back feature.
0 Loop back mode is disabled.
1 Loop back mode is enabled. When LOOP is set, the following occur:
• The UART_TX signal is set high.
• The UART_RX pin is disconnected
• The output of the transmitter shift register (TSR) is lopped back in to the receiver shift register (RSR)
input.
3-2 Reserved 0 Reserved
1 RTS RTS control. When AFE = 1, the RTS bit determines the autoflow control enabled. Note that all UARTs
do not support this feature, see the device-specific data manual for supported features. If this feature is
not available, this bit is reserved and should be cleared to 0.
0 RTS is disabled, CTS is only enabled.
1 RTS and CTS are enabled.
0 Reserved 0 Reserved
30
Universal Asynchronous Receiver/Transmitter (UART) SPRU997C–December 2009
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