Specifications

AN93
100 Rev. 0.9
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.
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.
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