Using Serial port for communication over longer distance

hi every1.
i am sohaib. i am currently working on a project to control different display units remotely. The prob dat i am facing is that i have been alloted with a very limited budget by the concerned authority. coming to the point.
6 microcontrollers are to be controlled via one singel pc. i can't go for Ethernet. Zilog supports Ethernet and comes with an Ethernet to serial converter as well but due to different reasons i can't go for that. Secondly i have decided to use Atmel 89C51. The prob is dat serial data can't be sent on longer distances exceeding 32.5m. The only solution dat i have now is to build a CAN. however i wanted to know if there's any other solution possible as i have a limited time period as well
plz anyone who has any idea do lemme know:
my email id is: 41sohaib@niit.edu.pk
Looking forward for +ive response.
Thanking you all.
CEB

Have you considered mulit-drop RS-485?
http://www.geocities.com/SiliconValley/Peaks/4125/rs485.pdf

You will be able to connect up to 32 devices over one twisted pair (half-duplex) or two twisted pairs (full-duplex), and distance is not a problem ..
Each of microcontrollers (slaves) will be assigned with unique addresses and your PC (master) will "talk" with them one-at-a-time ..

Regards,
IanP

Hi,
yes has a many different solutions. First is the RS485, this is classic solution for your problem, this is a multi client serial interface. Another choice is a multidrop RS232, but with high voltage. Other decision is a low speed optical network, with aglient trancivers and plastic fiber optic, the price is very good.
If you have only one direction communication, from PC to the controller, then you can use standard RS232, all is depend from the speed.
But all this is a only interfaces, not a protocol, you must have suitable communication protocol, for example :

byte 0 - start byte
byte 1 - recipient address
byte 2 - sender adress
byte 3 - package lenght
byte 4 - packeg type
byte 5..n - data
byte n+1 - CRC

and last, you must choice duplex, or simplex mode, and Master/Slave or equal priority for all but in this case you must look for the collision.