OT - Full duplex RS485 question !
Archiver
Posts: 46,084
Hi all,
I want to design a full-duplex multi-point RS485 system using for example the
LTC490 (or MAX490) RS485 transceiver chips on each node.However, I just
cannot understand how you multi-drop these devices ??
The chips have no transmit enable/disable pin so you cannot put the outputs
into a high impedance state, therefore, every device will have it's outputs
connected to the bus at the same time - surely this will cause bus contention
?(Before anyone says it, I know you can get devices with enable/disable pins
on-chip but I really must know how these devices are supposed to be connected
together first).
Thanks,
Darren
I want to design a full-duplex multi-point RS485 system using for example the
LTC490 (or MAX490) RS485 transceiver chips on each node.However, I just
cannot understand how you multi-drop these devices ??
The chips have no transmit enable/disable pin so you cannot put the outputs
into a high impedance state, therefore, every device will have it's outputs
connected to the bus at the same time - surely this will cause bus contention
?(Before anyone says it, I know you can get devices with enable/disable pins
on-chip but I really must know how these devices are supposed to be connected
together first).
Thanks,
Darren
Comments
WRONG
you must use MASTER - SLAVE protocol, and connect MASTER output to all
SLAVES input, any SLAVE output to MASTER input.
Full duplex communications are enable just if you will use 4 wires.
I already use that system several years without any problem. Protocol is
very important and I use
$-begin packet
adr-address 1byte
data-data
#-end packet
After power-up communication start with $$$ to reset all SLAVE units.
That's all
Best regards,
Damir
Original Message
From: <DAZLOGAN@a...>
To: <basicstamps@yahoogroups.com>
Sent: 13. studeni 2002 22:19
Subject: [noparse][[/noparse]basicstamps] OT - Full duplex RS485 question !
> Hi all,
>
> I want to design a full-duplex multi-point RS485 system using for example
the
> LTC490 (or MAX490) RS485 transceiver chips on each node.However, I just
> cannot understand how you multi-drop these devices ??
> The chips have no transmit enable/disable pin so you cannot put the
outputs
> into a high impedance state, therefore, every device will have it's
outputs
> connected to the bus at the same time - surely this will cause bus
contention
> ?(Before anyone says it, I know you can get devices with enable/disable
pins
> on-chip but I really must know how these devices are supposed to be
connected
> together first).
>
> Thanks,
> Darren
>
>
>
>
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