USB2SER question

Ron Czapala

I bought the USB2SER module to interface with my BS2 stamps and it works well.

I also tried to use it to connect to a Scott Edwards serial LCD (BPP-420L) which accepts TTL or RS232 signals.
The LCD displays garbage.

After searching the forums, it appears that the USB2SER outputs 3.3v rather than 5v TTL.
I am assuming that the LCD module needs a 5v signal to function (the LCD works fine usign the BS2 serout or using +/-12v from a PC serial port).

Does anyone have a different opinion on why the USB2SER will not drive the BPP-420L LCD?

Thanks!

JD

Ronczap,

The BASIC Stamp outputs a TTL level signal, so that would explain why the display would operate properly directly from the BASIC Stamp; looking at the manual of the BPP-420L is states TTL/CMOS can be used. Have you confirmed the inverted baud rate, 9600 or 2400 that is being used?

Snippet from the manual for the BPP-420:

Power requirements (BL off).................................4.8 to 5.5 Vdc @ 10mA
Power requirements (BL on)...............................4.8 to 5.5 Vdc @ 100mA
User connector .....................5-pin header; 0.025" posts on 0.10" centers
Connector pinout....................................................+5 GND SER GND +5
Serial input...............RS-232, or inverted TTL/CMOS, 9600 or 2400, N81
Buzzer output .............5V @ 25mA max; pulses approx. 100ms for BELL
Operating temperature.......................................0° to 50°C (32° to 122°F)
Serial data rates ............................................................2400 or 9600 bps

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Respectfully,


Joshua Donelson
www.parallax.com

Post Edited (Joshua Donelson (Parallax)) : 5/7/2009 4:12:47 PM GMT

Ron Czapala

Joshua,

Thanks for your response.

When I use the BS2 to drive the BPP-420 LCD·I use inverted 9600 (mode 16468).

The piggyback board on the LCD also lets you directly connect to standard PC·RS232 port (+12v/-12v) using the same connection (no line driver needed).

Both of those scenarios work fine.

Trying to use the USB2SER board does not work though. I imagine that the LCD needs a 5v TTL TX signal but the USB2SER is a 3.3v signal.

Chris Savage said...
"Please bear in mind that the USB2SER was a development tool used on the Propeller prior to its release and cannot bridge the gap between USB and RS-232 devices. The output is non-inverted and at 3.3V levels instead of the inverted +/-12V levels the key expects."

http://forums.parallax.com/showthread.php?p=746022

- Ron Czapala

Chris Savage

Ron, the key in Joshua's response was the word inverted...The SEETRON displays use inverted baud mode. Inherently, TTL devices typically use TRUE or non-inverted baud mode. If you were to run the TX/RX pins from the USB2SER through inverters, it should work. I don't recall if the display you're using has a single receive pin or uses a single pin for bi-directional communication, but the USB2SER would not be able to deal directly with a single bi-directional pin. I hope this helps. Take care.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Chris Savage
Parallax Engineering

Ron Czapala

Chris,
· The Seetron BPP-420 has three connection pins:· ground, +5v, and serial signal.

When I use a basic stamp to drive the LCD, ·I use inverted 9600 mode, but curiously the LCD also works when I directly connect the LCD's serial connection to my PC's DB9 serial port (pin 3). I use a vbscript program and MSCommLib.MSComm ActiveX control·(see code·below).

There is no inverted option on a standard PC RS232 port, correct?

The BPP420 somehow handles both the BS2 TTL inverted signal and also a direct RS232 serial connection on pin3 on the same wire.

I also have a Matrix Orbital LK204-25-WB (with onboard DB9) and it also displays garbage when I try to use the USB2SER module.
NOTE: I use a MAX233a when·connecting the LK204-25 to the Basic Stamp (non-inverted).

Since both displays work with the basic stamp 5v signal and neither work with USB2SER 3.3v, it seems like the voltage difference is the problem

Confusing...

-Ron

··· MSComm1.CommPort = comPort
··· MSComm1.DTREnable = False
··· MSComm1.EOFEnable = False
··· MSComm1.Handshaking = comNone
··· MSComm1.InBufferSize = 1024
··· MSComm1.InputLen = 0··
··· MSComm1.InputMode = comInputModeText
··· MSComm1.NullDiscard = False
··· MSComm1.ParityReplace = "?"
··· MSComm1.RThreshold = 1
··· MSComm1.RTSEnable = False
··· MSComm1.SThreshold = 0
··· MSComm1.Settings = "9600,n,8,1"
···
··· On Error Resume Next
··· MSComm1.PortOpen = True

JD

Ronczap,

It sounds like you are using multiple devices; can you please verify exactly what it is you are using?·Also, what controller you are trying to use also?

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Respectfully,


Joshua Donelson
www.parallax.com

Ron Czapala

Joshua,

I've basically been trying to get the USB2SER module to directly drive either of my LCD displays: Scott Edwards BPP-420L
or Matrix Orbital LK204-25-WB (with serial DB9 onboard) - no Basic Stamp.

The USB2Ser works fine with BS2 and BS2P stamps.
And the LCDs also work with the Basic Stamps:· BPP-420L (9600 inverted)·and LK204-25 (using MAX233a line driver·9600 non-inverted).

It is not a big issue, but it seems that the USB2SER·outputs 3.3v - sufficient for basic stamps but not for my LCDs expecting a 5v signal.

Anway, thanks for your responses. Maybe this thread will be helpful to people who are considering the USB2SER for driving devices other than microcontrollers...

- Ron