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TL16C752D: Can TL16C752D convert signals between UART and RS485?

Kazuya Nakai59
Guru 22355 points

Part Number: TL16C752D
Other Parts Discussed in Thread: THVD1500, THVD1406

Hello guys,

One of my customers is considering using TL16C752D for their new products.

At this moment, they have the following questions.
Could you please give me your reply?

Q.
They want to convert signals between UART and RS485 
because their CPU doesn't have RS-485 port and have UART port only.
Their product is connected to a device which has RS485 interface.
So they are looking for a device which can convert signals beteen UART and RS485.

Can TL16C752D convert signals between UART and RS485?
(Of course, they know a RS485 tranceiver,(ex. THVD1500) is needed to connect to external device).

Your reply would be much appreciated.

Best regards,
Kazuya. 

 

  • 0
    Prodigy 20 points

    Hi Kazuya,

    Currently i'm searching for similar solution. have you found any solution for this?

  • 0
    Guru 326440 points

    The purpose of the TL16C752D is to convert between an ISA bus (as used in old x86 systems) and UART.

    An RS-485 transceiver like the THVD1406 can be connected directly to the UART lines. (The THVD1500 would also needs the DE signal.)

  • 0 in reply to Clemens Ladisch
    Guru 22355 points

    Hello Clemens,

    Thank you very much for your reply.

    I understood that CPU can connect to external host with RS-485 on physical layer

    when THVD1406 is used.

    But the UART protocol is different from RS485 one (ex Modbus).

    So I think they need a bridge IC between UART protocol and RS485 protocol.

    Do you know any TI device which has the capability?

    Thank you again and best regards,
    Kazuya.  

  • 0 in reply to Kazuya Nakai59
    TI__Guru* 78042 points

    Hi Kazuya,

    We are currently on holiday. Please help give until next week for some feedback, thanks.

    Best Regards,

    Michael.

  • 0 in reply to Kazuya Nakai59
    Guru 326440 points

    RS-485 is primarily an electrical specification; a transceiver like the THVD1406 converts between the MCU's logic-level signal voltages and the RS-485 signal voltages.

    The RS-485 specification does not specify what protocol is transmitted with these voltage levels; there is no RS-485 protocol. Modbus uses the same framing as UART, so it would be possible to implement a Modbus-capable device with a UART. But whatever the protocol is, you need some device (typically a microcontroller) that implements that protocol.

  • 0 in reply to Clemens Ladisch
    Guru 22355 points

    Hi Michael and Clemens,

    Thank you very much for your reply.

    I will wait for Michael's feedback.

    Thank you again and best regards,
    Kazuya.

  • 0 in reply to Kazuya Nakai59
    TI__Guru* 81641 points

    Kazuya,

    Clemens is right. You don't need the TL16C752D device, this just takes parallel GPIOs from a processor and converts it to serial and vice versa (serial to parallel) in UART format. 

    You can just use an RS485 transceiver and connect the TX pin of the processor to the D pin RS485 tranceiver and the RX pin of the processor to the R pin of the RS485 transceiver.

    -Bobby

  • 0 in reply to BOBBY
    Guru 22355 points

    Hello Bobby,

    Thank you very much for your reply.

    Could I ask you the following additional question?

    I think one of the major protocol of RS485 is MODBUS RTU.
    Can UART protocol connect to MODBUS RTU protocol?

    Thank you again and best regards,
    Kazuya.

  • 0 in reply to Kazuya Nakai59
    TI__Guru* 81641 points

    Hi Kazuya,

    I'm not very knowledgeable on Modbus but UART and Modbus aren't the same in terms of software. TL16C752D would not fix this, it uses UART as the serial. You would need to use an MCU/processor that supports Modbus in terms of software. An RS485 transceiver should be able to perform the hardware function for Modbus but you yourself need to supply the Modbus software.

    -Bobby

  • 0 in reply to BOBBY
    Guru 22355 points

    Hi Bobby, Clemens,

    Thank you very much for your supports.

    Could I ask you one more additional question as the follow?
    The customer is considering using THVD1406 Clemens recommended.

    Q.
    Is there anything they should be careful about when they use THVD1406?

    Is it the receiver enabled timing after data sending finishing
    and is it suitable with the data sending timing from host?

    Thank you again and best regards,
    Kazuya.

  • 0 in reply to Kazuya Nakai59
    Guru 22355 points

    Hi Bobby, Clemens,

    Could I ask you again?

    In case of THVD1406, the wait time of direction changing from driver enabling to receiver enabling
    after D signal L -> H changing is 4us(min), 8us(typ), 14us(max).

    THVD1406 data rate is 500kbps(Max). 
    The time per 1bit is 2us.

    So I think the driver becomes disable if two consecutive H levels occur?
    Also I think the lowest data rate is limited by this automatic direction change function?
    Is my thought correct?

    Thank you again and best regards,
    Kazuya.

  • 0 in reply to Kazuya Nakai59
    TI__Guru* 81641 points
    Kazuya Nakai59 said:
    So I think the driver becomes disable if two consecutive H levels occur?
    Also I think the lowest data rate is limited by this automatic direction change function?
    Is my thought correct?

    No, externally you should have a pull up resistor and pull down resistor to set an external bias. When the driver disables, this bias will hold the bit high. 

    -Bobby