can't communicate with my BS2sx OEM.

Dgswaner

I connected my serial cable, as i did so I "zapped" it with static. since then I cannot communicate with the stamp.
the stamp is currently running the last program I uploaded. I'm assuming that this mans the PIC chip and voltage regulator circuitry are working. I thought I blew the Max232 chip as it's first in line to the port. I've replaced it and still the same thing. with the exact same cable, port and program, I can upload to different stamps. I know the problem is within the stamp. I tested the port and I have connectivity from the pins to the max232 chip. the max232 has power. I'm guessing that a vital resistor or cap. was fried. I don't know enough about the circuit to know where to go from here. can someone offer advice on how to solve this? I don't know how to test a capacitors or resistors. in circuit. of if you even can.

help would be greatly appreciated.

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A complex design is the sign of an inferior designer. - Jamie Hyneman, Myth Buster

JSWrightOC

AFAIK the BS2sx OEM uses a sprinkling of transistors to do the RS-232 translation - unless you bought the interpreter chip and other components, and substituted a MAX232 instead of the transistors. Can you elaborate on your configuration?

As for what might be dead...it is entirely possible that you fried one or both ports on the interpreter chip (A2 and A3 I believe are used for serial Tx and Rx), which would result in everything else working except the built-in serial port. However, it might only be the transistors (if your design has them) - if you have a logic probe (if not, make one!!) then you can verify if there is serial data making it to the BS2sx interpreter.

Also, something else to check...when you use the "Identify" in the Stamp IDE software, or try to download new firmware to the Stamp, does it reset your BS2sx? If so, then the portion of the circuit responsible for responding to the ATN line is working.

Dgswaner

it's a home brew BS2sx it does use the MAX232 chip for serial communication. when I try to use the identify it doesn't find the stamp the loop back and echo is all it says. when I try to upload a program it doesn't reset the stamp. and the code stays intact.

so your saying that possibly the "serial port" on the interpreter chip is blown not the max232 the other Dip 8 chip you have to buy from parallax is the Eprom isn't it?

thanks for the input.

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A complex design is the sign of an inferior designer. - Jamie Hyneman, Myth Buster

JSWrightOC

The bare minimum components to make an OEM Stamp circuit are the interpreter chip (in this case a pre-programmed SX28), a serial EEPROM (such as a Microchip 24FC128), a resonator (50MHz for the SX), and the RS-232 interface circuit, which normally consists of a handful of resistors (most in the form of a couple resistor packs) and three transistors. See this document. A source of regulated 5VDC is also required, of course. If I understand you correctly, you have replaced Q1, Q2, Q3, and the associated resistors, with a MAX232, correct? How are you handling the ATN line to reset the Stamp? How are you providing for the echo function? Can you produce a schematic or describe how you have things connected?

It sounds like you may have indeed fried the I/O pins on the interpreter chip responsible for serial communication - however, make sure that the Stamp is receiving the ATN signal to reset, otherwise it will never respond to an ID query or software download. If you use an LED and a logic gate to buffer the signal you can confirm that (1.) the Stamp is getting a reset signal and (2.) the Stamp is receiving serial data on the correct I/O pin. Either one should show as a brief flash of the LED, if you configure the polarity of the LED so that it is off in the normal resting state of the control line or I/O pin.

Aside from checking the I/O lines with a logic probe, you could try swapping the interpreter chip if you have a spare. It sounds like you have tried all other culpable suspects.

Let me know what you find!

Dgswaner

I swapped out the interpreter chip and still no go. I decided to scrap the bs2sx and I swapped it out for a propeller. If it were a quick fix I would keep it, but I'd rather spend time working getting the bot up and running on a propeller. Thanks for your help.

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A complex design is the sign of an inferior designer. - Jamie Hyneman, Myth Buster

JSWrightOC

Well I think we were close to finding the problem, especially if it wasn't the interpreter. You never did tell me what other circuitry was between the serial interface and the interpreter chip, so it could still be something simple. If you are no longer interested in the BS2sx-OEM, I would be glad to take the parts off your hands, and do a post-mortem!

Dgswaner

This BS2sx is a home brew from someone else. I didn't design it. and I don't have a schematic. I'll post a picture when I get to work. This board has been through WWII. but it's a really good design. I'd love to get a PCB layout for it.

I don't have a logic probe and I really don't know how to use one. if you pointed me to a source on how to make and use one I'm always up for learning. I wouldn't rule out a post-mortem.

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A complex design is the sign of an inferior designer. - Jamie Hyneman, Myth Buster

JSWrightOC

A logic probe is merely a circuit that drives one or two LEDs that show the logical state of the probe's input (usually true and complimentary), often fashioned into a pen-shaped device that allows you to probe various parts of the circuit you are checking. You could also use a bicolor LED. More elaborate designs may includ a pulse stretcher circuit, to alllow you to detect and see very brief pulses. Sometimes being able to listen to a rapidly-changing signal line with a small speaker is helpful. The range of options when building a logic probe are widespread, but the goal is the same - provide a means of monitoring the logic state of a signal, without adversely loading down the circuit you are trying to test. This means using a high-impedance CMOS device, ideally a 40xx series, 74HC, or 74HCT package, driving your LEDs or audio devices. Generally an input protection resistor should be included (to protect the gate from excessive voltages, such as if you accidentally touch it to an unregulated power supply that exceeds the voltage supply of the logic) and a very weak pull-down or pull-up resistor so that the probe defaults to a known state if a logic line is undriven. If you simply connected an LED to the part of the circuit you wish to monitor you might upset its operating characteristics and prevent it from functioning normally, as the LED requires considerably more current than a logic gate to operate. A logic probe is the most basic digital logic troubleshooting device, next to a volt-ohm meter or DMM.

If you want something more official, check here.

RobotWorkshop

Getting that BS2SX to work with a MAX232 shouldn't be that hard at all. I use the MAX232 (or MAX3232) for my projects with the OEM Stamps, SX processors and even the Prop.

For the BS2SX there is usually a small resistor between the RX and TX lines (along with a signal diode) on the side facing the PC. The other trick is that you need a pair of .1uf caps on the ATN line going to the stamp.
The wiring is similar on the Prop but the ATN signal is reversed. I know I made a post about this topic a quite a while back and i'll have to search through some old posts to find it if you are going to try the OEM stamp again and still have problems with it.

Robert