XR16L788 Exar Corporation, XR16L788 Datasheet - Page 16

• Manufacturer Part Number: XR16L788
• Description: High-performance 3.3V Octal Uart
• Manufacturer: Exar Corporation

Each UART in the 788 includes the infrared encoder
and decoder compatible to the IrDA (Infrared Data
Association) version 1.0. The input pin ENIR conve-
niently activates all 8 UART channels to start up in
the infrared mode. This global control pin enables the
MCR bit-6 function in every UART channel register.
After power up or a reset, the software can overwrite
MCR bit-6 if so desired. ENIR and MCR bit-6 also dis-
able the receiver while the transmitter is sending da-
ta. This prevents echoed data from reaching the re-
ceiver. The global activation ENIR pin prevents the in-
frared emitter from turning on and drawing large
amount of current while the system is starting up.
When the infrared feature is enabled, the transmit da-
ta outputs, TX[7:0], would idle at logic zero level.
Each UART channel provides an internal loopback
capability for system diagnostic purposes. The inter-
nal loopback mode is enabled by setting MCR regis-
ter bit-4 to logic 1. All regular UART functions operate
normally.
nals are re-configured. Transmit data from the trans-
4.3 I
4.4 I
NFRARED
NTERNAL
Figure 10
F
IGURE
L
M
OOPBACK
ODE
9. I
shows how the modem port sig-
Receive
IR Pulse
(RX pin)
RX Data
NFRARED
T X D ata
T ransm it
IR P ulse
(T X P in)
T
RANSMIT
0
Bit Time
B it T im e
0
1
1/16 Clock Delay
D
1
0
ATA
0
E
1
NCODING AND
C haracter
D ata B its
1
0
16
3/16 B it T im e
Data Bits
Character
Likewise, the RX [7:0] inputs assume an idle level of
logic zero.
The infrared encoder sends out a 3/16 of a bit wide
HIGH-pulse for each “0” bit in the transmit data
stream. This signal encoding reduces the on-time of
the infrared LED, hence reduces the power consump-
tion. See
The infrared decoder receives the input pulse from
the infrared sensing diode on RX pin. Each time it
senses a light pulse, it returns a logic zero to the data
bit stream. The decoder also accepts (when FCTR
bit-4 = 1) an inverted IR-encoded input signal. This
option supports active low instead of normal active
high pulse from some infrared modules on the mar-
ket.
mit shift register output is internally routed to the re-
ceive shift register input allowing the system to re-
ceive the same data that it was sending. The TX pin
is held at logic 1 or mark condition while RTS# and
DTR# are de-asserted, and CTS#, DSR# CD# and
RI# inputs are ignored.
0
0
0
1
R
ECEIVE
1
Figure 9
1
1
0
D
0
below.
ATA
1/2 B it T im e
1
1
XR16L788 OCTAL UART
D
IRdecoder-1
IrE ncoder-1
ECODING
REV. 1.1.4