Taskit RS232-ADC16, RS232-ADC24 User guide
RS232-ADC16/24
RS232-ADC16/24
Manual
Version 1.13
Copyright taskit GmbH 2009
www.taskit.de
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RS232-ADC16/24
Table of contents
1 Features..................................................................................................................3
2 Introduction.............................................................................................................3
3 Bringing into service................................................................................................4
4 Application Sample.................................................................................................5
5 Frame layout...........................................................................................................6
5.1 LRC calculation................................................................................................7
6 Commands..............................................................................................................8
6.1 Read Holding Registers...................................................................................8
6.2 Read Input Registers.......................................................................................8
6.3 Write Single Register.......................................................................................9
6.4 Write Multiple Registers...................................................................................9
6.5 Calibrate device.............................................................................................10
6.6 Save calibration data......................................................................................10
6.7 Error Response..............................................................................................11
7 Register description..............................................................................................12
7.1 Holding registers............................................................................................12
7.2 Input registers................................................................................................16
8 Techincal Details...................................................................................................17
8.1 RS232 connector...........................................................................................17
8.2 DSUB-25 connector.......................................................................................17
8.3 Electrical characteristics.................................................................................18
8.4 Reaction time.................................................................................................19
8.5 Power consumption........................................................................................20
8.6 Baud rate error...............................................................................................21
8.7 ADC................................................................................................................21
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RS232-ADC16/24
1 Features
● C8051F350/C8051F352 microcontroller at 3 – 49 Mhz
● RS232 interface
● Eight analog 16/24-bit inputs
● Eight digital 3.3V IOs (5V tolerant)
● Supply voltage range from 4.5V – 15V (absolut max. 20V)
● Provides 3.3V power supply for sensors
● Seperated analog ground
● Extended temperature range (-40°C – 85°C)
● Small instruction set
● Recalibration possible
● Access via C-library
2 Introduction
RS232-ADC16/24 device is designed to give simple access to external sensors
and peripherals over a standard RS232 connection. There is no need for any
additional drivers when using Windows, DOS or Linux systems. Microcontroller
only need a simple implementation of their UART interface.
Instructions send to the device have an human readable form allowing manual
traffic checking for debugging proposes. To integrate RS232-ADC16/24 into
your application, a C-library is provided with the device bearing the work of
protocol parsing and packet construction.
The device comes in two versions, one with 16-bit and one with 24-bit ADC
channels. These versions are named respectively to their ADC channel
resolution RS232-ADC16 and RS232-ADC24.
This document contains information about hardware issues, the software
protocol and resulting register mappings. It provides extra information for new
firmware versions 1.11 & 1.12.
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RS232-ADC16/24
3 Bringing into service
The following steps illustrate how to setup the device correctly.
1. Connect DSUB-9 adaptor to serial port.
2. Configure serial port to 115200 baud,
8N1 (8 bit data, no parity, 1 stop bit).
3. Power the device.
Use VIN (pin 24) and GND (pin 18) pins
of DSUB-25 connector. (15V max)
After this, a terminal program should display RS232-ADC's boot message.
Referring to the advice given in the boot message sending a questionmark will
produce a help text.
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RS232-ADC16/24
4 Application Sample
To illustrate the use of RS232-ADC16/24 – in special regard to VCC and VIN –
you might consider this schematic overview.
The task is to obtain sensor's data and transfer it to a monitoring software. In
case of critical or unusal conditions a nearby LED should indicate this.
Obviously, up to eight pairs of sensor and LED can be controlled using one
RS232-ADC16/24.
As described earlier, the device is powered via VIN at a maximum of 15V. The
device's internal voltage regulator provides 3.3V at VCC to power external
sensors. According to this, VCC should never be used to power RS232ADC16/24. Furthermore the range of the analog input (0 – 2.5V) has to be
taken in account.
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RS232-ADC16/24
5 Frame layout
This chapter specifies the used frame format. A frame does not contain more
than one command; each command is send together with all of its parameters.
Parameters larger than eight bits are expected in big-endian format, which
means the most significant byte (MSB) is send before the least significant byte
(LSB).
On serial line each byte is send with eight bits, one start bit and one stop bit.
There are no parity bits envolved in communication. The standard baud rate is
115200 baud. At the moment no handshaking is used because the host is
intended to wait for a response before sending a new request. Handshake can
be implemented in further versions as RS232-ADC16/24 provides a fully
populated RS232 connector.
A frame is encoded in an human readable ASCII format. Therefore each byte of
the frame's data is converted into two HEX digits. The converted frame then
consists of one start character, the command and parameters in HEX digits, a
packet LRC – also in HEX digits – and an end character.
Byte
1
Byte
2
Byte
3
Byte
4
Byte
5
... Byte
n-2
Byte
n-1
Byte
n
: Command Parameter
1
LRC <CR>
The end character is a "carriage return" (<CR>, '\r') resulting in hex code 0x0D.
Any addional "new line" (<NL>, '\n', 0x0A) is ignored by device and added to
any response.
Example : Read two ADC channels starting at 0x0001
Request :
:0400010002..<CR><NL>
Response :
:0404XXXXYYYY..<CR><NL>
Note : The first parameter is the byte count of read data, XXXX the value of
channel1, YYYY the value of channel2. LRC checking in requests can be
avoided by setting LRC to "..", replies always have a LRC although it is set to
".." in this example.
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RS232-ADC16/24
5.1 LRC calculation
The packet LRC is the two's complement of the sum over the packet's
parameter and command bytes.
LRC = -((∑data
n
) + command); with datan as binary byte values of the packet's
parameter list and command as binary value.
The correct LRC for the sample request above would have been 0xF8.
In regard to this including the LRC of a received packet itself into calculation will
result in a sum equal to 0, otherwise a transmission error has occured.
Note : Each binary data byte is transmitted as two HEX digits which have to be
transformed into binary form before adding them.
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