Specifications

AN93
94 Rev. 0.8
Figure 18. Asychronous UART Serial Interface Timing Diagram
The DCD and RI pins can be used as a hardware
monitor of carrier detect and ring signals. Additionally,
the INT
pin can be programmed to monitor the bits in
register U70 listed in Table 70. The RI, PPD, OCD, CID,
and RST bits are sticky, and the AT:I command reads
and clears these signals and deactivates the INT
pin if
INT
is enabled. A block diagram of the UART in the
serial interface mode is shown in Figure 19.
UART Time for Modem Receive Path (8N1 Mode)
UART Timing for Modem Transmit Path (9N1 Mode with 9th Bit Escape)
8-Bit Data
Mode
D0 D1 D2 D3 D4 D5 D6 D7
D0 D1 D2 D3 D4 D5 D6 ESCD7
Stop
Stop
Start
Start
t
RTS
t
RTH
RTS
CTS
RX
TX
t
RTS
t
CTH
9-Bit Data
Mode
Table 70. Register U70 Signals INT Can Monitor
Signal U70 Bit Function
DCD 0 Data Carrier Detect—active high (inverse of DCD
).
RI 1 Ring Indicate—active high (inverse of RI
).
PPD 2 Parallel Phone Detect.
OCD 3 Overcurrent Detect.
CID 4 Caller ID Preamble Detect.