This is the revision A version of the WireHost module.

WireHost Module (Revision A)

Table of Contents

1. Introduction

The WireHost module connects to both a RoboBricks2 bus and host computer via an RS-232 serial port. For computers that only have a USB port, a USB to RS-232 converter is required. The firmware in the WireHost module allows programs to be downloaded into other modules on the RoboBricks2 bus, such as one or more Controller28 modules.

In order to support long cables from the host computer to the robotic platform, the WireHost module uses inexpensive telephone cable with RJ11 connectors on both ends. The DB9RJ11 module is used to interface the RJ11 connector to a more standard female DB9 connector.

2. Programming

The WireHost module is connected to the host computer via 9-pin D connector using standard RS-274 voltage signalling levels (±12) running a 115200 baud with 8N1 (1 start bit, 8 data bits, No parity, and 1 stop bit.) If the host computer has a serial port, the connection can be made directly. If the host computer only has a

There are two supported modes -- terminal mode and host mode. In terminal mode, it is anticipated that the user will be talking to the WireHost module via a terminal emulator such as HyperTerminal on Windows® or MiniCom on Linux®. In host mode, it is expected that the use will be using a custom program that opens a serial connection to the WireHost module.

All terminal mode programs have the most significant bit cleared (i.e. plain ASCII) and all of the host commands start with the most significant bit set. This is summarized in the table below:

Bit Mode
7 6 5 4 3 2 1 0
0 x x x x x x x Terminal Command
1 x x x x x x x Host Command

Both terminal mode and host mode are discussed in separate sections below.

2.1 Terminal Mode.

Terminal Mode supports the following commands:

Command Response Description
A ii nn rr Programm the module with an id of ii set the node address nn. The response code rr is printed.
C rr Send the bus clear command out. This resets all of the modules on the bus into passive mode.
D rr Deselect the currently selected node. The response code rr is printed.
I Indentification information Print out the identification for the currently selected node.
J aaaa Jump into the code of the currently selected processor at aaaa.
S nn rr Select node nn and print response rr. If no node responds, '@' is printed.
X xx rr Transmit byte xx to the currently selected node. The response byte rr is printed. If no response is received, '@' is printed.
P pp 16 rows of 2 byte words Print out page pp of program memory from the currently selected processor.
R aaaa vv Read the byte at aaaa from the currently selected processor and display it as vv.
W aaaa vv Write byte vv into memory at address aaaa of the currently selected processor.
Z Identification for all modules. Sweep the bus and identify all modules plugged into the bus.
:xx... Program one line of Intel hex file into currently selected processor.

2.2 Host Mode

When the WireHost module is in host mode it can either be in master mode or slave mode. In master mode, it is control of the bus, it can select and deselect modules, send command bytes, and receive response bytes. In slave mode, it basically just forwards command bytes to the host so it can respond.

Command
Name		 Bit Direction Description
7 6 5 4 3 2 1 0
Transfer 0 x s s s r r r Send This transfers sss bytes to the the bus. aaaaaaaa through mmmmmmmm correspond to the sss bytes sent. All bytes are sent with the 9th bit clear, unless x is set in which case the first byte is sent with the 9th bit set and the remaining bytes are sent with the 9th bit clear. nnnnnnnn through zzzzzzzz correspond to the rrrr bytes received.
a a a a a a a a Send
... Send
m m m m m m m m Send
n n n n n n n n Receive
... Receive
z z z z z z z z Receive

2.3 Interprocessor Protocol

There are two PIC16F688 microcontrollers on the WireHost module. One microctonroller is called the host processor since it is permanently attached to the host computer via the MAX232 RS-232 voltage level conveter. The other microcontroller is permanently attached the to RoboBricks2 bus and is called the bus processor. There are seven wires that are connected between the processors This section documents the data communication protocol between the two processors.

The seven wires between the two processors are labeled P6 through P0 as summarized in the table below:

Label Host Pin Bus Pin Use Direction
P6 RA2 RA3 Handshake Host to Bus
P5 RA1 RA1 Handshake Bus to Host
P4 RA0 RA0 Strobe Host to Bus
P3 RC3 RC3 Data Host to Bus
P2 RC2 RC2 Data Host to Bus
P1 RC1 RC1 Data Bus to Host
P0 RC0 RC0 Data Bus to Host
Since the bus microcontroller needs to be able to generate a reset signal on N2, RA2 is used this purpose. Since RA2 is not avaiable for the interprocessor communciation, RA3 is used instead. The problem with RA3 is that it is an input only pin.

The host processor is always in controlling the data exchanges between the two processors. Basically data is extanged between the two processors two bits at a time. P3:2 are used to send data from the host processor to the bus processor. P1:0 are used to send data from the bus processor to the host processor. P4 is used to indicate that a command needs to be processed. P6:5 are used for handshaking between the two processors to synchronize data transfer.

The handshaking works as follows:

  1. The host processor places data on P4:2.
  2. The host processor toggles P6 to indicate that data is on P4:2.
  3. The bus processor notices that P6 has changed and reads the data off of P4:2.
  4. The bus processor shifts the P3:2 into its command shift register.
  5. If P4 is 1, the bus processor processes its command register.
  6. The bus processor places data on P1:0.
  7. The bus processor sets P5 to match P6 to indicate that data is on P1:0.
  8. The host processor notices that P5 matches P6 and reads the data off of P1:0.
This process repeats.

Currently there are only three commands that the host processor can issue and they are summarized in the table below:

Host Sends Bus Returns Description
9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0
0 s s s s s s s s s Send s ssss ssss out to the bus
1 0 e r r r r r r r r r Receive r rrrr rrrr from bus. e is 1 if no receive byte is present.
1 1 Strobe reset line on N3.

3. Hardware

The hardware consists of a circuit schematic and a printed circuit board.

3.1 Circuit Schematic

The schematic for the WireHost module is shown below:

WireHost Schematic

The parts list kept in a separate file -- wirehost.ptl.

3.2 Printed Circuit Board

The printed circuit board files are listed below:

wirehost_back.png
The solder side layer.
wirehost_front.png
The component side layer.
wirehost_artwork.png
The artwork layer.
wirehost.gbl
The RS-274X "Gerber" back (solder side) layer.
wirehost.gtl
The RS-274X "Gerber" top (component side) layer.
wirehost.gal
The RS-274X "Gerber" artwork layer.
wirehost.gml
The RS-274X "Gerber" mask layer.
wirehost.drl
The "Excellon" NC drill file.
wirehost.tol
The "Excellon" tool rack file.

3.3 WireHost Cable

The cable information can be found in the DB9RJ11 Module.

4. Software

There are two sets of firmware available for the Wirehost module.

The host firmware is available in the following files:

host.ucl
The µCL source code for the Host module.
host.asm
The Host module assembly code file.
host.lst
The Host module listing file.
host.hex
The µCL WireHost Intel® Hex file.

The bus firmware is available in the following files:

bus.ucl
The µCL source code for the Bus module.
bus.asm
The Bus module assembly code file.
bus.lst
The Bus module listing file.
bus.hex
The µCL WireHost Intel® Hex file.

5. Issues

The following fabrication issues came up:

Copyright © 2005-2007 by Wayne C. Gramlich. All rights reserved.