Patrick,

Patrick said “I see possibility of problems here... How will the sending 8051 now which command needs to be retransmitted if he does not keep track of which command has been acked and which one not? (CFR window mechansim of TCP..) As you allow multiple commands to be queued, and you have no way of matching an ACK to a certain command (or a NACK for that matter) how will you be able to retransmit that particular command that was not ACK'd (or NACK'd)?”

Well, That’s right there is a probability to miss some non crucial packets. Actually even in other protocols like isochronous USB there is such possibility. There are ways to prevent this (for example by adding a packet id), but for my project many of data packets are update information and it’s not very important to lose some of them. As I said before ACK and NACK have multiple purposes and CRC check is one of the purposes.

Erik,
Erik said “That is not correct, if you use a processor with hardware IIC such as the 668.” As I explained to russel, the project is much bigger than two 8051s, and I’ve already used hardware serials for other purposes, so what I said clearly in the original message, software I2C is demanding not hardware.

Erik said “Two USB slaves (all '51 implementations I know are slaves) can not talk to each other” I think you hasn’t read the message carefully, because it’s not that two USB 8051s are going to communicate in my project, but one 8051 communicate with computer.

Erik said “That is bull... skipping the supervisor is ridiculous, you will get all kinds of problems. Besides a supervisor is ~$1 and FIFOs are much more.”

have you read them ? especially #1
#1 http://www.8052.com/forum/read.phtml?id=64218
#2 http://www.8052.com/forum/read.phtml?id=64221
#3 http://www.8052.com/forum/read.phtml?id=64268
because the protocol has a cross checking feature so that if the other 8051 go to coma , then it will be reset. If you read this and still think that I should use supervisor please explain technically (why do you think cross checking feature of protocol is not enough)

Erik said “the FIFO solution is doable, but not cost efficient. “
Using FIFOs reduce communication time drastically, Using FIFOs 8051s are not interrupted by others while they are busy with their heavy jobs &….
Still don’t you think it worth the price ?

Thank you both,

Regards,
Ebrahim Vakilpour