I am using Docklight Scripting to put together a VBScript that communicates with a device via RS232. All the commands are sent in Hex.
When I want to read from the device, I send a 32-bit address, a 16-bit read length, and an 8-bit checksum.
When I want to write to the device, I send a 16-bit data length, the data, followed by an 8-bit checksum.
In Hex, the data that is sent to the device is the following:
AA0001110200060013F81800104D
AA 00 01 11 02 0006 0013F818 0010 4D
(spaced for ease of reading)
AA000111020006 is the protocol header, where:
- AA is the Protocol Byte
- 00 is the Source ID
- 01 is the Dest ID
- 11 is the Message Type
- 02 is the Command Byte
- 0006 is the Length Byte(s)
The remainder of the string is broken down as follows:
- 0013F818 is the 32-bit address
- 0010 is the 16 bit read length
- 4D is the 8-bit checksum
If the string is not correct, or the checksum is invalid the device replies back with an error string. However, I am not getting an error. The device replies back with the following hex string:
AA0100120200100001000000000100000000000001000029
AA 01 00 12 02 0010 00010000000001000000000000010000 29
(spaced for ease of reading)
Again, the first part of the string (AA00011102) is a part of the protocol header, where:
- AA is the Protocol Byte
- 01 is the Source ID
- 00 is the Dest ID
- 12 is the Message Type
- 02 is the Command Byte
The difference between what is sent to the device, and what the device replies back with is that the length bytes is not a "static" part of the protocol header, and will change based of the request. The remainder of the string is broken down as follows:
- 0010 is the Length Byte(s)
- 00010000000001000000000000010000 is the data
- 29 is the 8-bit Check Sum
The goal is to read a timer that is stored in the NVM. The timer is stored in the upper halves of 60 4-byte NVM words.
The instructions specify that I need to read the first two bytes of each word, and then sum the results.
Verbatim, the instructions say:
Read the NVM elapsed timer. The timer is stored in the upper halves of 60 4-byte words.
Read the first two bytes of each word of the timer. Read the 16 bit values of these locations:
13F800H, 13F804H, 13808H, and continue to 13F8ECH.
Sum the results. Multiply the sum by 409.6 seconds, then divide by 3600 to get the results in hours.
My knowledge of bits, and bytes, and all other things is a bit cloudy. The first thing I need to confirm is that I am understanding the read protocol correctly.
I am assuming that when I specify 0010 as the 16 bit read length, that translates to the 16-bit values that the instructions want me to read.
The second thing I need to understand a little better is that when it tells me to read the first two bytes of each word, what exactly constitutes the first two bytes of each word?
I think what confuses me a little more is that the instructions say the timer is stored in the upper half of the 4 byte word (which to me seems like the first half).
I've sat with another colleague of mine for a day trying to figure out how to make this all work, and we haven't had any consistent results with our trials.
I have looked on the internet to find something that would explain this better in the context being used.
Another worry is that the technical data I am using to accomplish this project isn't 100% accurate in their instructions, and they have conflicting information or skipping information throughout their publication (which is probably close to 1000 pages long).
What I would really appreciate is someone who has a much better understanding of hex / binary to review the instructions I've posted, and provide some feedback on my interpretation of the instructions provided, and provide any information.
