xr16m780 Exar Corporation, xr16m780 Datasheet - Page 23

• Manufacturer Part Number: xr16m780
• Description: 1.62v To 3.63v High Performance Uart With 64-byte Fifo
• Manufacturer: Exar Corporation

REV. 1.0.0
an interrupt is pending from any channel. The M780 will stay in the sleep mode of operation until it is disabled
by setting IER bit-4 to a logic 0.
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. Also, make sure the RX pin is idling HIGH or “marking” condition
during sleep mode. This may not occur when the external interface transceivers (RS-232, RS-485 or another
type) are also put to sleep mode and cannot maintain the “marking” condition. To avoid this, the system design
engineer can use a 47k ohm pull-up resistor on each of the RX input.
If the address lines, data bus lines, IOW#, IOR#, CS# and modem input lines remain steady when the M780 is
in sleep mode, the maximum current will be in the microamp range as specified in the DC Electrical
Characteristics on
current can be up to 100 times more. If not using the Power-Save feature, an external buffer would be required
to keep the address and data bus lines from toggling or floating to achieve the low current. But if the Power-
Save feature is enabled (PwrSave pin connected to VCC), this will eliminate the need for an external buffer by
internally isolating the address, data and control signals (see
could cause wasteful power drain. The M780 enters Power-Save mode when this pin is connected to VCC and
the M780 is in sleep mode (see Sleep Mode section above).
Since Power-Save mode isolates the address, data and control signals, the device will wake-up only by:
The M780 will return to the Power-Save mode automatically after a read to the MSR (to reset the modem input
CTS#) and all interrupting conditions have been serviced and cleared. The M780 will stay in the Power-Save
mode of operation until it is disabled by setting IER bit-4 to a logic 0 and/or the Power-Save pin is connected to
GND.
The M780 has the wake up interrupt. By setting the FCR bit-3, wake up interrupt is enabled or disabled. The
default status of wake up interrupt is disabled. Please
Write-Only” on page 31.
2.17.2
2.17.3
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a receive data start bit transition (HIGH to LOW) at the RX input or
a change of logic state on the modem or general purpose serial input CTS#, DSR#, CD#, RI#
Power-Save Feature
Wake-up Interrupt
page
45. If the input lines are floating or are toggling while the M780 is in sleep mode, the
1.62V TO 3.63V HIGH PERFORMANCE UART WITH 64-BYTE FIFO
23
See ”Section 4.5, FIFO Control Register (FCR) -
Figure 1
on
page
1) from other bus activities that
XR16M780