AN2262 Motorola / Freescale Semiconductor, AN2262 Datasheet - Page 8

• Manufacturer Part Number: AN2262
• Description: Wireless HC08 Modem
• Manufacturer: Motorola / Freescale Semiconductor

AN2262/D
User RS485 Ports
8
The user RS485 current loop serial port looks simple but is relatively more
complicated to connect and configure. It consists of:
Two-wire or four-wire topology can be selected. In two-wire topology, both
RS485 transmitter and receiver share one pair of wires and cannot transmit and
receive at the same time. Such operation is call half-duplex communication.
Level shifter U5 has separate receiver enable and driver output enable pins
which are connected to MCU pins PTC5 and PTC6. The RS485 transmitter
must be enabled prior to transmission and disabled after the transmission is
finished. Jumper JP3 connects the RS485 receiving lines to the transmitting
lines creating the two-wire topology. Connect JP3’s 1-2 and 3-4.
Signal
Signal
Name
Name
•
•
•
RXD
DSR
GND
RXD
DSR
GND
TXD
CTS
DTR
TXD
CTS
DTR
RTS
RTS
Table 2. RS232 Signal Mapping on J2 (Female) DB-9 Connector
Table 1. RS232 Signal Mapping on J3 (Male) DB-9 Connector
A level shifter, U5
Required capacitor, C26
Optional resistors, R25 and R28
Direction
Direction
Wireless HC08 Modem
Signal
Output
Output
Output
Signal
Output
Output
Output
Input
Input
Input
Input
Input
Input
—
—
Data terminal ready
Data terminal ready
Request to send
Request to send
Data set ready
Data set ready
Transmit data
Transmit data
Clear to send
Clear to send
Receive data
Receive data
Function
Function
Ground
Ground
Mapping on J3
Mapping on J2
(Female)
(Male)
3
2
7
8
4
6
5
2
3
8
7
6
4
5
MOTOROLA