On 2017-02-18 15:12, Clemens Gruber wrote:
On Sat, Feb 18, 2017 at 11:35:51AM +0100, Maarten Brock wrote:
On 2017-01-30 12:12, Fabio Estevam wrote:
> From: Fabio Estevam <fabio.estevam@xxxxxxx>
>
> When userspace passes the SER_RS485_RTS_ON_SEND flag it means that the
> CTS_B pin should go to logic level **high** before the transmission
> begins.
So setting the SER_RS485_RTS_ON_SEND flag sets CTS_B active high
during
send.
No, CTS_B is an active-low output, so SER_RS485_RTS_ON_SEND leads to a
logic level low CTS_B during transmit.
So, the word 'high' (emphasized by me) in your original mail actually
should
have been 'low'.
> When userspace passes the SER_RS485_RTS_AFTER_SEND flag it means that
> the CTS_B pin should go to logic level low after the transmission
> finishes.
And setting the SER_RS485_RTS_AFTER_SEND flag sets CTS_B active low
after
send ?
No, this also sets CTS_B to logic level low, but after the transmission
ends.
I don't get it. First, isn't CTS an input instead of an output?
On the i.MX6, CTS_B is an output and can be connected for example to
the
transceive-enable input of a RS-485 transceiver.
The name is confusing, I guess this is due to the different meaning in
DTE/DCE mode.
And if I follow this through and want CTS_B high during a transmit
only then
I must set both SER_RS485_RTS_ON_SEND and SER_RS485_RTS_AFTER_SEND.
If you want CTS_B to be logic high during transmit, then you only set
SER_RS485_RTS_AFTER_SEND and clear SER_RS485_RTS_ON_SEND.
On our board we invert the signal in hardware, so we can use the
default
setting (only SER_RS485_RTS_ON_SEND), then go through the inverter to
the active-high transmit-enable input of the transceiver.
Clemens
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