XR16M598 Datasheet, PDF (21/58 Pages) Exar Corporation – 1.62V TO 3.63V HIGH PERFORMANCE OCTAL UART WITH 16-BYTE FIFO

XR16M598
REV. 1.0.0
1.62V TO 3.63V HIGH PERFORMANCE OCTAL UART WITH 16-BYTE FIFO
2.15 Sleep Mode with Auto Wake-Up
The 598 supports low voltage system designs, hence, a sleep mode is included to reduce its power
consumption when the chip is not actively used.
All of these conditions must be satisfied for the 598 to enter sleep mode:
■ no interrupts pending for all 8 channels of the 598 (ISR bit-0 = 1)
■ SLEEP register = 0xFF
■ modem inputs are not toggling (MSR bits 0-3 = 0)
■ RX input pin of all 8 channels are idling HIGH
The 598 stops its crystal oscillator to conserve power in the sleep mode. User can check the XTAL2 pin for no
clock output as an indication that the device has entered the sleep mode.
The 598 resumes normal operation by any of the following:
■ a receive data start bit transition (HIGH to LOW)
■ a data byte is loaded to the transmitter, THR or FIFO
■ a change of logic state on any of the modem or general purpose serial inputs: CTS#, DSR#, CD#, RI#
If the 598 is awakened by any one of the above conditions, it will generate an interrupt. If the interrupt for the
event that woke up the 598 is not enabled, then a special wake-up interrupt occurs where reading the interrupt
status register will return a "no interrupt" indication. For example, there is a change of state on the CTS# input
that wakes up the 598, but the MSR interrupt is not enabled. Reading the interrupt status register will return a
value indicating that there are no pending interrupts and will clear the wake-up interrupt.
The 598 will return to the sleep mode automatically after all interrupting conditions have been serviced and
cleared. If the 598 is awakened by the modem inputs, a read to the MSR is required to reset the modem inputs.
In any case, the sleep mode will not be entered while an interrupt is pending in any channel. The 598 will stay
in the sleep mode of operation until it is disabled by setting SLEEP = 0x00.
A word of caution: owing to the starting up delay of the crystal oscillator after waking up from sleep mode, the
first few receive characters may be lost. The number of characters lost during the restart also depends on your
operating data rate. More characters are lost when operating at higher data rate.
21