XR17D158 datasheet(21/72 Pages) EXAR

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XR17D158

REV. 1.2.1

UNIVERSAL (3.3V AND 5V) PCI BUS OCTAL UART

2.2.6

SLEEP [31:24] (default 0x00)

Each UART can be separately enabled to enter Sleep mode through the Sleep register. 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 D158 to enter sleep mode:

• no interrupts pending (INT0 = 0x00)

• divisor is a non-zero value for all channels (ie. DLL = 0x1)

• sleep mode is enabled (SLEEP = 0xFF)

• modem inputs for all channels are not toggling (MSR bits 0-3 = 0)

• RX input pins for all channels are idling HIGH

The D158 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 D158 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 D158 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 D158 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 D158 will stay in the sleep mode of operation until it is disabled

by setting Sleep = 0x00. In this case, the octal UART is awaken by any of the UART channel 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 XR17D158 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.

2.2.7

Device Identification and Revision

There are two internal registers that provide device identification and revision, DVID and DREV registers. The

8-bit content in the DVID register provides device identification. A return value of 0x28 from this register

indicates the device is a XR17D158. The DREV register returns an 8-bit value of 0x01 for revision A with 0x02

equals to revision B and so forth. This information is very useful to the software driver for identifying which

device it is communicating with and to keep up with revision changes.

SLEEP Register

Individual UART Channel Sleep Enable

Ch-6

Ch-7

Ch-5 Ch-4 Ch-3 Ch-2 Ch-1 Ch-0

Bit-7 Bit-6 Bit-5 Bit-4 Bit-3 Bit-2 Bit-1 Bit-0

XR17D158 Datasheet(PDF) 21 Page - Exar Corporation

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