communication between 2 microcontrollers using uart

[tejashs]

communication between 2 P89V51RD2 microcontrollers using uart

if i need to communicate between 2 P89V51RD2 microcontrollers using uart with range of
a) 1 meter and below
b) 10 meters and above
what are the things i should take care of
can i directly connect the RX and TX pins for 1m range, my circuits already have max232.
my speed of transmission is 4800baud

 

[klystron]

Did you search EDA for RS232 cable length?

 

[tejashs]

ok i got it that 12meters is maximum distance
can i make a serial bus from 1 8051 and have a couple of drop to other 8051's(one 8051 feeding a couple of 8051s)?
do i need a max232 at all for connecting between 28051's for short distances of a feet or so?
and is it suffucient if i use max232 or should i go for max485?
speed is not a primary concern i can even manage with 1200 baud

 

[Kurenai_ryu]

for any thing over 1m (3feet) i suggest interconnect by rs232 (two max232 at both ends)
my tests showed that rs232 could work until 40m (over 100 feet) but it's over the recomendation/regulation but it worked any way...
for over 10m(30 feet) it's always recomended to use to RS485/RS422 it will work up 1000 meters (1km)

for something lower than 1m you can connect directly... but if you need to connect/disconnect, make use of a intermediate buffer or some kind of proteccion...

 

[tejashs]

Kurenai_ryu i do not understand what you mean by this

but if you need to connect/disconnect, make use of a intermediate buffer or some kind of proteccion...

and is it possible to make something like this using rs232???

 

[Kurenai_ryu]

mmm sorry my bad english...
i mean if you have, mmm, a complete functional system, with 2 micrcontroller near that you need to have communicated... maybe they are to close (lower than 1m) you don't need any buffer. (but it's suggested)

if you have a system with only one microcontroller. and plan to have some kind of plugable/unplugable extra device (like and hmi or anything that use the other microcontroller) the fact of plug-in and unplug should be taken in consideration.

now for the other stuff.

Rs232 is know for been peer-to-peer comunicacion, just one host and one slave (that in case that you need duplex communication)

if you are planning to have one microcontroller as master (connected to PC) and several slaves (master-slave comunication) i suggest to use some kind of bus...
rs485 seems logical, specially if the slaves are at some distance...

if every thing is very close, i suggest to use/implement I2C (i know that's something ver different to rs232 and usart and so... but i2c is maded just for that, to communicate many devices even in the same board.)

for Rs232 you could investigate about the Daisy-chain implementation...

also to address slaves in RS485 take a look at the modbus specification... for address data sizes, checksums etc....