Thanks for the reply Pylon and sorry for the delayed response...
That's even easier, get a USB2RS232 adapter, the ones with a Prolific PL2303 are only a few bucks.
I actually found one of these type adapters laying around the lab here and
I started to build an interface to the RJ4 connector and power required by my device
but have not gotten it working yet.
The MAX 3222 doesn't generate a +/- 12V signal but a +/- 5V signal (according to the datasheet) but this should be OK for most applications.
The MAX 3222 doesn't have an RXD pin. How did you connect the Arduino to this chip?
I used the same circuit as the serial device that I am interfacing with
uses. The only difference is that the I am connecting to the Arduino where that
device interfaces to an FPGA...
Not sure how to post a JPG on this forum as a picture is worth a thousand words
but here is a breakdown of the pins of the MAX32222 connections
Pin1 - EN/ - VSS
Pin2 - C1+ - 0.1ufd Cap (other side connected to pin4)
Pin3 - V+ - 0.1ufd Cap (other side connected to VSS)
Pin4 - C1- - 0.1ufd Cap (other side connected to pin2)
Pin5 - C2+ - 0.47ufd Cap (other side connected to pin6)
Pin6 - C2- - 0.47ufd Cap (other side connected to pin5)
Pin7 - V+ - 0.1ufd Cap (other side connected to VSS)
Pin8 - T2OUT - N/C
Pin9 - R2IN - VSS
Pin10 - R2OUT - N/C
Pin11 - T2IN - N/C
Pin12 - T1IN - Arduino D1
Pin13 - R1OUT - Arduino D0
Pin14 - R1IN - To Serial Device TXD (an RJ4 connector pin1)
Pin15 - T1OUT - To Serial Device RXD (an RJ4 connector pin3)
Pin16 - GND - VSS
Pin17 - VCC - 3.3V
Pin18 - SHDN/ - 3.3V
For what it is worth, the RJ connector on the Serial device has the following
pinout as referenced by the device:
Pin1 - RS232 In
Pin2 - +12V
Pin3 - RS232 Out
Pin4 - Gnd
The +12V and Gnd are supplied by an external power adapter and I have tied
the GND of this to the Arduino ground.
As I stated before, I am able to read data coming from the device but unable to
send data to the device.
A new observation is that the signal on D1 (TXD) dies when the Max3222 is
connected to the D0 (RXD) line while the D0 (RXD) line receives data just fine.
When I disconnect the MAX3222 pin 13 from the D0 (RXD) line, the D1 (TXD) signal is no
longer dead (as seen on my scope) and I can then send data to the device.
In this condition, the data from the device (when a button is pressed) is seen on
the MAX3222 pin 14 but it is not read in hyper terminal with pin 13 disconnected from D0.
To carry this another step further, I reconfigured the MAX3222 so that all pins (except pin14)
were connected to see if the D1 (TXD) line was getting dragged down by the device but
found that in this configuration D1 was also dead.
For an additional sanity check, I replaced the MAX3222 with another new part and as long
as D0 (RXD) is connected to the MAX3222 pin 13, the D1 (TXD) line is dead...
Seems like there is some sort of contention on the TXD line when the RXD line
is connected to the arduino...