XR17D152 Datasheet, PDF (18/68 Pages) Exar Corporation – UNIVERSAL (3.3V AND 5V) PCI BUS DUAL UART

XR17D152
UNIVERSAL (3.3V AND 5V) PCI BUS DUAL UART
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REV. 1.2.0
2.2.6 SLEEP [31:24] - (default 0x00)
The 8-bit Sleep register enables each UART separately to enter Sleep mode. Sleep mode reduces power
consumption when the system needs to put the UART(s) to idle. All of these conditions must be satisfied for the
D152 to enter sleep mode:
• no interrupts pending (INT0 = 0x00)
• divisor is a non-zero value for both channels (ie. DLL = 0x1)
• sleep mode is enabled (SLEEP = 0x03)
• modem inputs for both channels are not toggling (MSR bits 0-3 = 0)
• RX input pins for both channels are idling HIGH
The D152 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 D152 resumes normal operation by any of the following:
• a receive data start bit transition (logic 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 D152 is awakened by any one of the above conditions, it will return to the sleep mode automatically after
all interrupting conditions have been serviced and cleared. If the D152 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 from any channel. The D152 will stay in the sleep mode of operation until it is disabled
by setting Sleep = 0x00. In this case, the dual UART is awaken by any of the UART channel on from a receive
data byte or a change on the serial port. The UART is ready after 32 crystal clocks to ensure full functionality.
Also, a special interrupt is generated with an indication of no pending interrupt. Reading INT0 will clear this
special interrupt. Logic 0 (default) is disable and logic 1 is enable to sleep mode.
Important: The XR17D152 is a versatile device designed to operate with different VCC (core power supply)
and VIO(PCI bus I/O power supply). However, the VCC and VIO must be equal (VCC = VIO) for the sleep
mode to reduce power consumption. Any difference in these voltages will result in high currents, when placed
in sleep mode. If sleep mode is used, it is recommended that both VCC and VIO be powered by the PCI bus
VIO power pins. If sleep mode is not used, there is no concern about high currents whether VCC = VIO or VCC
> VIO. In any case, VCC should never be less than VIO.
SLEEP Register
Individual UART Channel Sleep Enable
Bit-7 Bit-6 Bit-5 Bit-4 Bit-3 Bit-2 Bit-1 Bit-0
Rsvd Rsvd Rsvd Rsvd Rsvd Rsvd Ch-1 Ch-0
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