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Determining Transceiver Input Type

Determining Transceiver Input Type

(OP)
I’m trying to find an rs485 transceiver with an input type of TTL but it doesn’t seem that any of the datasheets explicitly say they are TTL. Are there any other keywords that will identify the part as such? For datasheets that do have a partial schematic of the chip internals, the topologies do not look like TTL.

RE: Determining Transceiver Input Type

Strictly speaking the drivers are analog devices that convert 3.3 or 5V logic levels to the 485 standard drive levels. There is no need to know whether or not the devices have "TTL inputs".

Just ask:
Do they have the 3.3 or 5V inputs you need?
Do they have the speed required for your proposed data rate?
Do they have the temp spec you require?
Do they have any needed slew rate limiting for RFI mitigation?
Do they have built in termination or not.
Do they have static event mitigation added. Is it enough for your application?
Do they have any optional features like standby?
Can it drive the network load you have.

Those are the questions a designer usually cares about with regard to comm drivers.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Determining Transceiver Input Type

(OP)
Thank you for your help. It is tough to know which specs are relevant but I think you've cleared up the issue. A colleague told me that they needed to be TTL inputs but he must have been mistaken.

RE: Determining Transceiver Input Type

Likely what is important is that they are simply standard logic levels. i.e. 5V or 3.3V and that was morphed into "TTL".

TTL is considered high above 2.0V and low below 0.8V. With a comm driver controlled by a micro the speed with which the processor pins change state is orders of magnitude higher than the signalling rate so any timing issues that could be caused by the rise/fall times mapped to the 0.8/2.0V trigger points would be irrelevant anyway.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Determining Transceiver Input Type

The : MAX1490EBEPG+ Description:
RS-422/RS-485 Interface IC Isolated RS-485/422 Data Interface
Will be a good match
any question : daveross100@gmail.com

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