RS-232/I²C-Adapter & Parallel I/O ModuleSubmitted to Parallax by Guenther Daubach
Figure 1 – The RS-232/I²C-Adapter
This module is used to control external components via the I²C bus using simple command sequences sent and received via an RS-232 port from an application software running on a PC or a PDA, for example. The on-board MAX-232 level shifter allows direct interfacing to a standard COM port. The RS-232/I²C-Adapter acts as an I²C master, and performs the most frequently used read/write operations via the bus without the need to let the application software handle the I²C protocol. When the application sends one of the “macro command sequences”, the adapter takes care of generating the start condition, transmitting the address plus the R/W bit, transmitting/receiving data bytes plus setting/reading the acknowledge but, and finally generating the stop condition. All this is performed transparently to the application software.
Besides this, the adapter also lets the application software directly “talk” to the I²C bus in order to allow communications with I²C devices that require non-standard sequences, by using the adapter’s “low-level commands”.
In addition, the RS-232/I²C-Adapter also comes with a reed relay that can be controlled by two dedicated commands. This allows the application software to initialize various devices via the I²C bus before finally turning on the power supply for some other components, for example. Besides this, the relay may also be used as a general-purpose isolated output.
There are also available four non-isolated outputs, and eight non-isolated inputs that can be set/read by specific adapter commands. The eight inputs also clock individual 16-bit counters that may be read/reset by designated adapter commands.
Optionally, a timer may be activated that resets the I²C-Adapter when no more commands are received via RS-232 within the specified time-out period.
A special “Monitor Mode” is also available turning the RS-232/I²C-Adapter into an I²C monitor, that can be used to analyze an I²C bus system. In this mode, the adapter “listens” to the I²C bus, and sends information about all activities it recognizes to the application software via RS-232, without interfering the I²C bus communication by itself.
Three LEDs indicate the status of the RS-232/I²C-Adapter, the activities on the I²C bus, and on the RS-232 lines.
The RS-232/I²C-Adapter is based upon a Ubicom/Parallax SX-28 microcontroller, clocked at 50 MHz. Single, pre-programmed chips are available for customers who want to integrate the RS-232/I²C-Adapter’s functionality into their own hardware design (see below).
Specifications:
Power Supply: 5V DC, stabilized and filtered
Relay Output: 1A, 250 V DC (maximum ratings)
Parallel Outputs: TTL (0/5V), max. 30 mA sink/source
Parallel Inputs: TTL (0/5V), Schmitt-Trigger characteristics.
RS-232: 115.2 kBaud, 8N1 (handshake is handled by the command protocol)
I²C: Transfer rate can be set to 20, 50, or 100 kbit/s
Dimensions: 2” * 2” (50mm * 50mm)
Connectors: Two male 14-pin headers, 0.1” (2.54 mm) spacing
 Available Modules:
RS-232/I²C-Adapter: Assembled and tested.
RS-232/I²C-Adapter Kit: Includes PCB, and all components.
RS-232/I²C-Adapter Parts Kit: Includes PCB, SX controller, and a 50 MHz resonator.
RS-232/I²C-Adapter Chip: Includes the pre-programmed SX controller.
All modules are shipped with a CD-ROM containing the documentation, schematics, assembly instructions, and a sample VB application project.
Parallel/Analog I/O Board
Figure 2 – The Parallel/Analog I/O Board
This is a companion board for the RS-232/I²C-Adapter. It allows to piggy-back the adapter via two 14-pin header sockets. An on-board standard SUB-D 9 male connector is provided to directly interface the RS-232/I²C-Adapter’s serial port to a COM port.
It also contains the necessary components (four reed relays, and eight opto-isolators) to convert the RS-232/I²C-Adapter’s I/O lines into isolated I/O lines.
In addition, the board comes with a Philips PCF8591 I²C chip which extends the I/O capabilities of the RS-232/I²C-Adapter to four 8-bit analog inputs, and one 8-bit analog output.
Due to an on-board DC/DC converter, the module accepts any DC supply voltage from 8V to 38 V, un-stabilized. The stabilized DC/DC converter output voltage (5V) is available to supply other components that are connected to the Parallel/Analog I/O Board.
Specifications:
Power Supply: 8…38 V DC, non-stabilized.
1 Relay Output: The RS-232/I²C-Adapter relay output is fed-through to two separate connectors.
4 Relay Outputs: 1A, 250 V DC (maximum ratings)
8 Inputs: Opto-isolated, 5…30V, common minus.
4 A/D inputs: 0…5 V, 8 bit resolution, single-ended or differential inputs.
1 D/A output: 0…5 V (no resistive load), 8 bit resolution.
Power output: 5 V DC stabilized, 500 mA max., fused with over-voltage protection.
Dimensions: 4” * 3.2” (100mm * 80mm)
Connectors: Clamp plugs, 0.15” (3.81mm) spacing
 Available Modules:
Parallel/Analog I/O Board: Assembled and tested, including matching clamp plugs.
Parallel/Analog I/O PCB: PCB only .
Figure 3 – The Parallel/Analog I/O Board with a piggy-backed RS-232/I²C-Adapter & Parallel I/O Module.
All modules are shipped with a CD-ROM containing the documentation, schematics, and assembly instructions.
Guenther Daubach
MDA EDV-Beratung GmbH
Im Eulenflug 25
D-51399 Burscheid, Germany
Tel./Fax: +49 2174 – 785 931
email: info@mda-burscheid.de
home: http://www.g-daubach.com
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