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CAN add-on
Parity
Data bits
Stop bits
Baud rate
Special features of RS485
40
– Parity: In order to recognize an error or incorrect data during the transfer,
a parity bit can be transferred at the same time. The parity can be even
or odd or you can have no parity bit at all.
– Data bits: the active data to be transferred may be 5...8 bits long.
– Stop bits: The number of stop bits can be set to 1, 1½ or 2. Here the num-
ber of stop bits depends on the number of data bits:
•
5 data bits: 1 or 1½ stop bits.
•
6...8 data bits: 1 or 2 stop bits.
– Baud rate: The physical data are between 35 Baud and 2.304MBaud;
when using an RS-232 interface the maximum Baud rate is 115.2
kBaud.
The Baud Rates are derived by the clock rate of the module; the basic
clock rate has a frequency of 2.304MHz. Based on this fact, every Baud
rate is possible that can be derived by an integer division of the basic fre-
quency. The divisor can have values between 1...0FFFFh. The follow-
ing table shows some common Baud rates and their divisors:
Baud rate
Divisor
dez.
2304000
1
1152 000
2
460800
5
230400
10
115200
20
57600
40
38400
60
Via a RS485 interface more than 2 participants can communicate with each
other. (Contrary to the RS232 interface). With RS485 interfaces a bus can be
set up.
Consider the following:
– There is no handshake, because a handshake is only possible between
2 participants.
– The interface must know if it should write to the bus or get data from the
bus (RS485_SEND).
9.3.2 Programming
Functionality and programming of the interface depend on this controller. The
controller is easily programmed with ADbasic instructions:
Range
Initialization
Receiving and transmitting of data
Write and read access
to the controller register
The instructions are in the include file <ADWGCAN.INC>. More information can
also be found in the ADbasic manual and the online help.
Baud rate
hex.
19200
0001h
9600
0002h
4800
0005h
2400
000Ah
1200
0014h
600
0028h
300
003Ch
Fig. 30 – RS-xxx: Baud rates
Instructions
RS_INIT,
RS485_SEND, READ_FIFO,
WRITE_FIFO
GET_RS,
ADwin-Gold USB / ENET, manual version 3.8, October 2005
ADwin
Divisor
dez.
hex.
120
0078h
240
00F0h
480
01E0h
960
03C0h
1920
0780h
3840
0F00h
7680
1E00h
RS_RESET
SET_RS
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