How to have four PIC16F87x chips on one RS232 bus ?

Hi, I am investigating the possibillity to have 4 PIC 16F877 connected
to the same PC on a RS232 'bus'.
I am using MAX220CPE, can they be connected in parallell or will they go
up in flames ?


> -----Original Message-----
> From: pic microcontroller discussion list


> [mailto:PICLIST@MITVMA.MIT.EDU] On Behalf Of Bob Ammerman
> Sent: Tuesday, 3 July 2001 9:53 a.m.
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [PIC] RS232 BUS ?


>
> If all of the following are true:
>
> - The PC is going to act as a master
>
> - The F877's will only speak when spoken to
>
> - The F877's are physically close to each other (ideally sharing the same
> power supply).
>
> Then there is a low-cost simple way to be your network...
>
> Take the TD signal from the PC and route it thru the RS232 to TTL channel of
> the MAX220 to the RD signals of all four PICS.
>
> Connect a signal diode (IN4148 is fine) from the TD pin of each of the PICs
> to the TTL to RS232 channel of the MAX220. The cathode of the diode should
> be connected to the PIC pin.
>
> Connect a 10k resistor from the junction of all the diodes with the MAX220
> pin to the positive supply rail.
>
> Connect the output of the TTL to RS232 channel of the MAX220 to the PC.
>
> All the F877's will be able to 'hear' the PC.
>
> The PC will be able to 'hear' any F877.
>
> As long as only one F877 at a time 'talks' everything will be well.
>
> If more than one F877 tries to talk at the same time the PC will get garbled
> data, but no hardware damage will be done.
>
> Bob Ammerman
> RAm Systems
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