Hi Jose,

Thank you very much for your response.

Note: I apologise in advance before typing the post. Please ex-cuse me If you find my words jarring.

- A soft uart is slow so a 10 uart at the same time will be slooooooow

Are still living with those old 12 cycle micros runing at 12MHz or something? If one uses a better derivate say P89V51RD2 running at 40MHz in 6 cyle mode some other derivate in single cycle mode I don't think 10 devices in software bit banged UART are a problem. I never said my scheme will cater to all 10 devices simultaneously I have kept saying one device at a time and other devices on hold by handshaking signal. Even if a multi drop RS485 or RS422 scheme is used only one of those 10 devices can communicate with PC. well I don't see any significant advantage with RS485. Even with RS485 on PC side some software and some protocol has to be there to take care of comuunication with those 10 devices.

- As option i suggested the use of a external hard UART

I don't see any significant advantage in using Hard UART except for increased cost on hardware and size of hardware. Whats the harm in handling one device at a time and putting others on hold using handshake as in my scheme. Anyways for PC side communication you have only one channel and you can't send simultaneously the data to or from all those 10 devices due to this PC communication channel bottleneck.

- You say that he implement put some protocols.. but may be he can't if the 'slaves' devices are done
The protocol has nothing do with slaves slave will just communicate normally. The protocol will be acting in between PC and the 8051 shown in my shematic.

- You say is 'cheapest' and i think as some one says: "Cheap is the thing that you know how it cost before starting" and may be you know the components cost but you must design the PCB, and the soft and make all work

I know the whole issue is the word "CHEAPEST" that I used in my post. Believe me I didn't really mean it I mean a CHEAP option and certainly not CHEAPEST a mistake made in fast typing or poor english I leave it to you to decide.

- The PC soft must be special and you can't use the standard programs like i.e. flip or others.
Who says a standard program will be usefull if RS485 is used you will need a special software even if a RS485 is used.

Now ball is in your court Please Justify your Rating.

Thanks & Regards,
Prahlad Purohit