Disappearing Key Assignments

[ijabbott]

(01-02-2020 04:56 PM)Sylvain Cote Wrote:  

(01-02-2020 03:55 PM)cdmackay Wrote:  please forgive me going off-topic a little, but can you explain what the two sets of 8 LEDs denote, on the tester?
Is the left set of 8 looking in one direction, the right set in the other?

Yeah, I asked myself the same question when I received the tester, I am used to only have one set of LEDs.

After some experiments, I discovered that the lights were used as follow:

Code:

LEDS   Description   LEDS
0  1  1:DCD | 6:DSR  0  1
0  1  2:RXD | 7:RTS  0  1
0  1  3:TXD | 8:CTS  0  1
0  1  4:DTR | 9:RI   0  1

In my test, when both cables are plugged but no software is running the tester show this:

Code:

0  1   Description   0  1
X  -  1:DCD | 6:DSR  X  -
X  -  2:RXD | 7:RTS  X  - 
X  -  3:TXD | 8:CTS  X  -
X  -  4:DTR | 9:RI   -  -

note: X means LED is lighted on and - means LED is not lighted

When I start clupdate, then the tester show this:

Code:

0  1   Description   0  1
X  -  1:DCD | 6:DSR  X  -
X  -  2:RXD | 7:RTS  -  X
X  -  3:TXD | 8:CTS  X  -
-  X  4:DTR | 9:RI   -  -

Then I start the python test program, after the port is open I see:

Code:

0  1   Description   0  1
-  X  1:DCD | 6:DSR  -  X
X  -  2:RXD | 7:RTS  -  X
X  -  3:TXD | 8:CTS  -  X
-  X  4:DTR | 9:RI   -  -

Then the LEDs on RXD & TXD are moving back and forth from 0 to 1 when there is transmission going on.

Hope it clarify things a bit.

The 0s and 1s seem to be transposed, but apart from that it looks OK. Logic 0 is "asserted" (space) in RS-232, and logic 1 is "deasserted" (mark). The quiescent state of RXD and TXD (when no characters are being sent) is logic 1.

From the set-up you posted earlier, the Prolific adapter (controlled by clupdate) is acting as the DTE (data terminal equipment), and the FTDI adapter via the Null Modem dongle (controlled by the Python test program) is acting as the DCE (data circuit-terminating equipment). The Null Modem dongle will cross over RXD & TXD, CTS & RTS, DSR & DTR, and wire DCD to DSR at each end. So on the tester:

• DCD shows the state of DTR output by the FTDI before the Null Modem
• RXD shows the state of TXD output by the FTDI before the Null Modem
• TXD shows the state of TXD output by the Prolific
• DTR shows the state of DTR output by the Prolific
• DSR shows the state of DTR output by the FTDI before the Null Modem
• RTS shows the state of RTS output by the Prolific
• CTS shows the state of RTS output by the FTDI before the Null Modem
• RI is not passed through the tester (it would normally be output by a real modem)