Serial Communication in Advanced Ladder

Open Communications Overview

The Open Communications Port function provides a way to open any of the available serial ports that are not otherwise in use by the

The modes/protocols available are

Generic ASCII, used for bar code readers, weight scales, and other devices which could work with a simple ASCII terminal program
Modbus A popular, de-facto standard protocol that allows industrial devices from multiple manufacturers to easily share data in real-time. Can be run over serial communications such as RS-232 and RS-485, as well as Ethernet. Modbus over Ethernet is usually referred to as Modbus TCP/IP.RTU RTU - Remote Terminal Unit - A microprocessor-based device that monitors and controls field devices, that then connects to plant control or SCADA (supervisory control and data acquisition) systems., for either Modbus Master or Modbus Slave communications
Modbus ASCII, for either Modbus Master or Modbus Slave communications

Serial Ports opened with this function will remain open until the Close Communications Port function [Close Communications Port] is used or the OCS controller is put into STOP mode. Any Open function that is used when the selected port has already been opened by another Open Port function will change the parameters accordingly.

Note on OCS as a serial Modbus Master: Even though it is still possible to build highly customized serial Modbus Master communications using logic, Modbus Master functionality has been largely supplanted by the much easier-to-use . For any single port, the Open function and the Protocol Configuration cannot be used at the same time.

Note on OCS as a serial Modbus Slave: Using this function, along with the Modbus Slave function, is the only way to enable serial Modbus Slave communications.

Note on MJ1 programming port: The MJ1 port is the default Cscape programming port for nearly every OCS, though USB and Ethernet programming are also automatically available on most OCS products. Using the Open function on MJ1 will open it for the specified parameters and close it to Cscape programming use. Closing the MJ1 port with the Close Communication Port in Advanced Ladder function will disable whatever Open parameters were last used and will re-open the port to Cscape programming. If it is absolutely required to use MJ1 for communications and an RS-232 programming port is also required for Cscape access, it is possible to reassign the programming port to another port in the System Menu of the OCS controller. See System Settings in

Settings from Registers: It is possible to “hard code” the settings by leaving this box unchecked and using the dropdown selections for each parameter. Alternately, the settings may be obtained dynamically from an array/registers by checking this box. Specifying “Settings From Registers” and an array element/register will use the values in 8 consecutive elements/registers for these settings. See remaining parameters for values to use when this box is checked.

Port: The serial port to open with this function. Options will vary per OCS model and may include MJ1, MJ2, MJ3, and COM. Older OCS models may include PORT 1, PORT2, and CN1. For “Settings From Registers”:

0 = MJ1
1 = MJ2 (or CN1 for NX)
2 = CN1 (for QX only)
3 = MJ3

Baud Rate: Select the baud rate to match the device being communicated with. For “Settings From Registers”:

0 = 300 baud
1 = 600 baud
2 = 1200 baud
3 = 2400 baud
4 = 4800 baud
5 = 9600 baud
6 = 19200 baud
7 = 38400 baud
8 = 57600 baud
9 = 115200 baud
10 = 14400 baud
11 = 28800 baud
12 = 10400 baud

Parity: Select the parity to match the device being communicated with (None, Odd, Even) . For “Settings From Registers”:

0 = None
1 = Odd
2 = Even

Data Bits: Select the data bits to match the device being communicated with (7, 8) . For “Settings From Registers”:

2 = 7 Data Bits
3 = 8 Data Bits

Stop Bits: Select the stop bits to match the device being communicated with (1, 2) . For “Settings From Registers”:

0 = 1 Stop Bits
1 = 2 Stop Bits

Handshake Handshaking is an automated process that sets parameters for communication between two different devices before normal communication begins. Much like the way a human handshake sets the stage for the communication to follow, the computing handshake provides both devices with the basic rules for the way data is to be shared between them. These rules can include transfer rate, coding alphabet, parity, and interrupt procedure.: Options will vary with OCS used. For RS-232 comms, this should match wiring and the device being communicated with (None, Xon/Xoff, Hardware). For the RS-485 An EIA standard that specifies electrical characteristics of drivers and receivers for use in serial communications. Electrical signaling is balanced and multipoint systems are supported. standard, “Multidrop Full” should be used for RS-485 4-wire connections and “Multidrop Half” MUST be used for 2-wire connections, in conjunction with proper DIP switch settings on some models. For “Settings From Registers”:

0 = None
1 = Xon/Xoff
2 = Hardware
3 = Multidrop Full
4 = Multidrop Half
5 = Radio Modem

Protocol: The desired protocol for which to open the port

1 = CsCAN
2 = Generic ASCII
3 = Modbus RTU
4 = Modbus ASCII
5 = Modbus TCP (Only for XL series with HE-XEC option board)

Mode: The standard to use with this function, restricted to RS-232 and RS-485 unless an option card is installed.

0 = RS232
1 = RS485
2 = Modem
3 = Ethernet
4 = Fiber A
5 = Fiber B
6 = GSM Dual
7 = GSM Quad
8 = Radio 900MHz
9 = Radio Zigbee

Power Flow

The Open Communications Port function executes immediately and entirely as soon as it receives power from the incoming rung. The port may be immediately used for configured communications assuming success.

The Open Communications Port function will execute on every scan that it has received power from the incoming rung.

The Open Communications Port function will pass power flow to the next function on the rung unless a port that does not exist is specified (possible with dynamic settings).

There is no need for any further functions to exist to the right of the Open Communications Port function on the rung. The function’s result is considered an output.

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ASCII Character Codes

The following are 8-bit ASCII ASCII - American Standard Code for Information Interchange - ASCII-coded characters are single-byte values in the range of 0 (zero) to 127. Codes in the range 128 to 255 are not defined by the ASCII standard, but rather by the equipment manufacturer. characters and their character codes.

Char	Dec	Hex A base-16 numbering system which uses the symbols 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F for numeral.
NULL Null Termination - To place a NULL character (character code 0) at the end of ASCII data. Some functions require NULL Termination to be able to determine the end point of the ASCII data since that data may vary in length from one time to the next.	0	00
SOH	1	01
STX	2	02
ETX	3	03
EOT	4	04
ENQ	5	05
ACK	6	06
BELL	7	07
BS	8	08
HT	9	09
LF	10	0A
VT	11	0B
FF	12	0C
CR	13	0D
SOH	14	0E
SI	15	0F
DLE	16	10
DC1	17	11
DC2	18	12
DC3	19	13
DC4	20	14
NAK	21	15
SYN	22	16
ETB	23	17
CAN	24	18
EM	25	19
SUE	26	1A
ES1	27	1B
FS2	28	1C
GS	29	1D
RS	30	1E
US	31	1F
(SPC)	32	20
!	33	21
"	34	22
#	35	23
$	36	24
%	37	25
&	38	26
'	39	27
(	40	28
)	41	29
*	42	2A
+	43	2B
,	44	2C
-	45	2D
.	46	2E
/	47	2F
0	48	30
1	49	31
2	50	32
3	51	33
4	52	34
5	53	35
6	54	36
7	55	37
8	56	38
9	57	39
:	58	3A
:	59	3B
<	60	3C
=	61	3D
>	62	3E
?	63	3F
@	64	40
A	65	41
B	66	42
C	67	43
D	68	44
E	69	45
F	70	46
G	71	47
H	72	48
I	73	49
J	74	4A
K	75	4B
L	76	4C
M	77	4D
N	78	4E
O	79	4F
P	80	50
Q	81	51
R	82	52
S	83	53
T	84	54
U	85	55
V	86	56
W	87	57
X	88	58
Y	89	59
Z	90	5A
[	91	5B
\	92	5C
]	93	5D
^	94	5E
_	95	5F
`	96	60
a	97	61
b	98	62
c	99	63
d	100	64
e	101	65
f	102	66
g	103	67
h	104	68
i	105	69
j	106	6A
k	107	6B
l	108	6C
m	109	6D
n	110	6E
o	111	6F
p	112	70
q	113	71
r	114	72
s	115	73
t	116	74
u	117	75
v	118	76
w	119	77
x	120	78
y	121	79
z	122	7A
{	123	7B
\|	124	7C
}	125	7D
~	126	7E
DEL	127	7F

Manufactured Specified..........................128-255..............80-FF

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