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5.9.3 Control Signals - RTS, CTS, DTR, DSR, DCD, RI
Switching times for RTS and CTS
Request to Send (RTS)
Clear To Send (CTS)
LZT 123 7589 R1A
5. SYSTEM CONNECTOR INTERFACE
UART1 control signals are active low and need a standard interface IC,
such as the MAX3237, to generate standard RS232 levels.
UART1 converted signals, together with DGND, RD and TD form a
9-pin RS232 data port.
RTS and CTS are capable of transmitting at 1/10
speed for data rates up to 460 kbit/s (byte-oriented flow control
mechanism).
When hardware flow control is not used in communications between the
application and the radio device, RTS and CTS must be connected to each
other at the radio device.
The table below shows the switching times.
Parameter
Time from Low to High level
Time from High to Low level
Used to condition the DCE for data transmission. The default level is high
by internal pull up.
The application must pull RTS low to enable data transmission from the
radio device. Similarly, the radio device asserts CTS low, indicating it is
ready to receive data transmission from the host.
Parameter
Application driving impedance
Input capacitance
Input resistance (pull-up)
CTS is asserted by the DCE to indicate that the host (DTE) may transmit
data. When CTS is high, the host (DTE) is not permitted to transmit data.
The table below shows the load characteristics for this signal.
Parameter
Application load capacitance
Application load resistance
th
of the data transmission
Limit
< 2 µs
< 2 µs
Limit
< 100
< 2 nF
100 k to DGND
Limit
< 500 pF
1 M
38
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