Uart Operation In Low-Power System States - Motorola DragonBall MC9328MX1 Reference Manual

Table 27-29. UART1 Test Register 1 and UART2 Test Register 1 Description (Continued)
Name
SOFTRST Software Reset—Indicates the status of the software reset (SRST).
Bit 0

27.8 UART Operation in Low-Power System States

The UART's serial interface will operate as long as the 16x bit clock generator is provided with the
PerCLK1. The RXEN, TXEN and UARTEN bits are set by the user and provide software control of
low-power modes.
When in DOZE state, the UART's behavior depends on the DOZE bit. If the DOZE bit is negated and the
system is in DOZE state, the UART serial interface is operational. If the system is in DOZE state and the
DOZE bit is asserted, the UART transmitter and receiver operations are halted.
If the DOZE state is entered with the DOZE bit asserted when the UART's serial interface is receiving or
transmitting data, the reception/transmission of the current character is completed and signal to the far-end
transmitter/receiver to stop sending/receiving. The control/status/data registers do not change when
entering or exiting low-power modes.
The following UART interrupts wake the ARM920T processor from STOP mode:
• RTS
• IrDA Asynchronous WAKE (AIRINT)
• Asynchronous WAKE (AWAKE)
The UART_CLK_EN bit (UCR1_1/UCR1_2) enables the clock inputs to the UART module. If the control
bit is set to 0, it abruptly enables the clock inputs to the UART module. To get maximum power
conservation when the module is shut off, make sure that the above clock control bit is set to 0. Setting the
UARTEN (UCR1_1/UCR1_2) bit to 0 only shuts off the receiver and transmitter logic and the associated
clocks.
When an asynchronous WAKE interrupt exits the ARM920T processor from STOP mode, make sure that
a dummy character is sent first because the first character may not be received correctly. After the settling
time of the USB_PLL, actual characters can be sent to the UART. Even though the dummy character is
written to RxFIFO, just ignore it.
MOTOROLA Universal Asynchronous Receiver/Transmitters (UART) Modules
UART Operation in Low-Power System States
Description Settings
0 = No software reset
1 = Generate software reset
27-51