xr16c854iv Exar Corporation, xr16c854iv Datasheet - Page 20

• Manufacturer Part Number: xr16c854iv
• Description: Quad Uart With Rx/tx Fifo Counters And 128-byte Fifo
• Manufacturer: Exar Corporation

XR16C854/854D
2.97V TO 5.5V QUAD UART WITH 128-BYTE FIFO
The infrared encoder and decoder are enabled by setting MCR register bit-6 to a ‘1’. When the infrared feature
is enabled, the transmit data output, TX, idles at logic zero level. Likewise, the RX input assumes an idle level
of logic zero from a reset and power up, see
Typically, the wireless infrared decoder receives the input pulse from the infrared sensing diode on the RX pin.
Each time it senses a light pulse, it returns a logic 1 to the data bit stream. However, this is not true with some
infrared modules on the market which indicate a logic 0 by a light pulse. So the 854 has a provision to invert
the input polarity to accomodate this. In this case user can enable FCTR bit-2 to invert the input signal.
The 854 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 854 to enter sleep mode:
The 854 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.
2.19
■
■
■
■
no interrupts pending for all four channels of the 854 (ISR bit-0 = 1)
sleep mode of all four channels are enabled (IER bit-4 = 1)
modem inputs are not toggling (MSR bits 0-3 = 0)
RX input pins are idling at a logic 1
Sleep Mode with Auto Wake-Up
F
IGURE
Receive
IR Pulse
(RX pin)
RX Data
TX Data
Transmit
IR Pulse
(TX Pin)
12. I
NFRARED
0
Bit Time
Bit Time
0
1
1/16 Clock Delay
T
RANSMIT
1
0
Figure
0
1
Character
Data Bits
D
1
12.
ATA
0
20
Data Bits
3/16 Bit Time
Character
0
E
0
NCODING AND
0
1
1 1
1
0
R
0
ECEIVE
1/2 Bit Time
1
1
IRdecoder-
IrEncoder-1
D
ATA
D
ECODING
xr
REV. 3.0.1