Basic stamp SX OEM Chip cannot communicate
thomasschubert
Posts: 15
Hi, I have the SX basic stamp OEM version on my PCB board. Im using an RS232 chip for the signals. I am not looping back RX and TX, is this required, if so how is this done with the RS232 Drivers.!.
I have loop back which works OK, but no echo and no communication with the SX chip.
I have checked with a scope, the basic stamp is polling the E2Prom. I do not have the .01uf caps in series with the reset pin as this circuit looks like a voltage divider and I have 5 volts from the RS232 chip.
so in a nut shell, do I need the echo circuit, what else may be causing no communications.
Thanks All
I have loop back which works OK, but no echo and no communication with the SX chip.
I have checked with a scope, the basic stamp is polling the E2Prom. I do not have the .01uf caps in series with the reset pin as this circuit looks like a voltage divider and I have 5 volts from the RS232 chip.
so in a nut shell, do I need the echo circuit, what else may be causing no communications.
Thanks All
Comments
http://www.robotworkshop.com/robotworkshop/projects/parallax/BS2p40OEMschematic.pdf
I use the MAX232 with the OEM Stamp chip from Parallax. If you are interested here is the docs used to build the board:
http://www.robotworkshop.com/robotworkshop/projects/parallax/BS2p40oem.pdf
Hope this helps,
Robert
You may need the capacitors in the reset circuit since some serial ports hold DTR active when open and that would force the Stamp to stay reset until the serial port is closed. It depends on how the I/O drivers are written. Most drivers allow the program to control the DTR line explicitly.
Hi, I have placed the caps on ATN, used a diode and resistor for the echo circuit, still no communications. I did notice when trying to connect to the stamp the NVAM stopped unitll polling was complete, this may just be the reseting of the chip. This is strange as the NVAM is being polled on the Data and Clock lines. SO, SI & ATN all seem to toggl and do somthing. Is there a timming issue somewhere.
I have used the SX chip before just with standard ASM, I have my RTC pin floating, I do recall sometimes that can cause a problem.
Thanks
Thomas
Did you get a chance to review the schematic I posted earlier in this thread? I connect the RTCC pin to ground and know that works. The schematic uses a MAX232 for the RS232 connection. If you follow that it should work ok.
Robert
I have tried the RTC to ground, still nothing. I have just tried a new SX chip, still nothing. Im wondering if the NVRAM is not working will I get the same error "Basic Stamp Not Found". Theres not much here to go wrong lol.
Thanks for the Schematic, that works fine.
- What is the exact part # for the memory chip you're using?
- Do you have a 4.7K or other pull-up on the SDA line?
- What voltage are you running 5V, 3.3V, or what? A 5V supply should be good. Anything less and you could be running into a brownout issue.
- What are you using as a power supply? Is it a set of batteries, unregulated wall wart, or a nice stable 5V supply?
- Have you double checked all the connections against the schematic for the SX stamp and also the schematic I provided?
- What is the exact version of the Stamp chip you are trying to use. If it is the BS2SX are you using the DIP version of the chip or the Surface mount version? In case you weren't aware the pinout if different on the two package styles. If you are wiring things up for the other version it won't work!!
- What are you using for a resonator? Is it setup the same as the stamp modules? There is often a small cap and resistor used there.
- Have you tried swapping the RX and TX lines? If they are crossed you may still get the echo back ok but it will never find the stamp.
If you have a picture of your setup we may be able to spot something wrong.
Best Regards,
Robert
I have attached a screen print of the SX basic stamp circuit, its shows the chip, nvram, and the main connections.
The I2C device is a 24FC128-I/ST
The SX chip used is SX28AC/DP-G 0947 Has Parallax written on it.
Everything is 5V, using a standard linear regulator. The only thing external is the serial coms interface which is from the parallax schematic.
I have the 10K bias resistor but not a capacitor on the 50MHZ resonator which seems to be working.
Hope you can help.
Thanks
Thomas
- Are you using the $4 SX28 processor or the $12 BS2SX OEM stamp chip?? The regular SX28 chip lacks the BASIC Stamp 2SX Interpreter code. There are several people over the years that have gotten them mixed up because both have SX in the names and the BS2SX happens to be programmed into an SX28 chip. We really need to know for sure what chip you have. If it is a regular SX28 chip then it won't have the BASIC Stamp Interpreter code on it and you'll never get a response from the BASIC Stamp tools.
- The other comment I have is that on your schematic you have a 4-pin header going to the OSC pins as well as VCC and GND. That would be for an SX-Key (or SX-Blitz) programmer used to program the firmware of an SX28 chip directly. You'd never want that on a board using a BASIC Stamp chip since you could overwrite the Interpreter code by mistake and turn a $12 chip into a regular $4 SX processor. You'd only add that 4-pin header for projects using the SX28 processor directly. In that case you'd either be programming in assembly code or SX/B which is a compiled BASIC code. It all resides with the SX chip itself and doesn't require the external memory chip like the BASIC stamp does.
Best Regards,
Robert
Thanks for the reply. I have the SXKEY connector as an option to the Basic stamp. Some projects I'm developing need higher speeds.
The SX chips I purchased are the OEM Interpretor versions. Given the schematic could you see anything that could cause this issue. I am supprised that I cant get any response at all from the device.
Last Friday I put an SX Basic stamp on a bread board, just wired up the communications and resonator only, no NVRAM and still had no luck.
Thanks
Thomas
If you use the OEM BASIC Stamp chip then you have to have the EEPROM chip installed. That is where the tokenized BASIC program code is stored. Only Parallax can say for sure but I'd expect that if you leave off the EEPROM chip then the startup code within the Stamp may hang and it may not respond. I've never tried that but expect that you'd have issues leaving off that part. That is part of the minimal configuration for the BASIC Stamp.
The schematic doesn't show the clock circuit or the RS-232 interface so I can't tell if that is ok or not. All I can say is that I know the schematic with the MAX232 that I posted early on does with with the OEM Stamps. It has the loopback resistor, a diode, and a MAX232. Are you using a MAX232 chip for the RS-232 signals? One thing to note is that with the loopback resistor installed you will get the loopback response even if the RX and TX lines are crossed at the Stamp. I ran into that the first time I used an OEM stamp on a project. Just swapping the RX and TX lines on the Stamp fixed it. Whenever you see and RX and TX the next question is always RX and TX in relation to what? There should always be an out/in listed for both signals since they sometimes refer to the other end and end up being opposite of what you expect.
Robert
Dave