
[2] Signal state
Only difference between "hardware flow ctrl" and "no hardware flow ctrl" is
that signals CS and DR are deemed always ON if "no hardware flow ctrl" is
selected.
(1) After channel is open
hardware flow ctrl no hardware flow ctrl
-------+-----------------------+---------------------
SD
RD
RS ON <-
CS don't care
ER ON <-
DR ON
CD
(2) While sending data
hardware flow ctrl no hardware flow ctrl
-------+-----------------------+---------------------
SD send data <-
RD
RS ON <-
CS flow control don't care
ER ON <-
DR external device status ON
CD
(3) While receiving data
hardware flow ctrl no hardware flow ctrl
-------+-----------------------+---------------------
SD
RD receive data <-
RS flow control(*1) ON
CS
ER error report(*2) <-
DR external device status ON
CD
(*1) RS becomes OFF when receive buffer is full and returns to
ON when there are free space in the buffer
(*2) ER becomes OFF when receive data overflows the receive
buffer. This happens, for example, when data transmission
does not stop even if RS is brought OFF to request
stopping data transmission.