TI E2E Community
SN75155 RS-232 Driver Issue
I am trying to use this as just a driver, but I cant see anything on my hyper terminal. The chip works fine as a receiver, since I can send text from my hyper terminal to the chip and see the output on an LCD screen. I have the chip running at 5VDC. Is there anything else I need to add to the circuit to get the chip to work as a driver?
The SN75155 requires dual supplies; the range is +/-4.5V to +/-15V. Do you have a -5V on pin 1 (VCC-)?If you only have a +5V supply, I suggest a single supply devices , like the TRSF3221E .
Regards,Ronald MichallickLinear Applications
TI assumes no liability for applications assistance or customer product design. Customer is fully responsible for all design decisions and engineering with regard to its products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning Customer's design. If Customer desires engineering services, the Customer should rely on its retained employees and consultants and/or procure engineering services from a licensed professional engineer (LPE).
Right now, I had it running at 5VDC on pin 1. Would I need to have a 15VDC powersupply hooked up to pin 1 in order for this thing to operate properly?
There should be a negative supply on PIN1 (VCC-) and a postive supply on pin 8 (VCC+).
Pin 1 = -5V and Pin 8= +5V is good.Pin 1 = -12V and Pin 8= +12V is betterPin 1 = +5V and Pin 8= +5V is not good.
Sorry, yes that is how its set up, -5 on pin 1, +5 on pin8.I have the signal from my microprocessor going to pin 2, and pin 7 going to the RS232 connection on my PC.No other parts hooked up to the circuit. Still doesnt seem to work, even at the 12VDC =/
Now that the supply voltage have been verified, it is time to measure the voltages on the 'DA" and 'DY' pins. Measure the 'DA" input voltages. Verify the VIH is at least 2V and VIL is less than 0.8V.
If the 'DY' voltages meet the VOH and VOL values on page 4 of the data sheet, check the RS232 wiring to the PC.If the voltages are bad, try unplugging the RS232 cable and measure again. If still bad, try changing the SN75155.
I hooked up a scope to the DA and DY pins to make sure the voltages were correct. DA was between 0-5VDC. DY was a little high with the rs232 connected to it, but removed, it was within the acceptable range. I still see nothing on my hyper terminal. When I checked the DY signal, it looks like it is stuck high, at around 5VDC. The DA signal is sending the message, so the levels go between 0-5VDC. I went through 10 of the chips that I had, to make sure that the one wasnt bad, but they all showed the same values. My circuit configuration is: -5VDC to pin 1, +5VDC to pin 8, Serial in from Microprocessor to pin 2, serial out to pin 7, GND of the serial connected to pin 4. Should I have the GND pin also put to -5VDC?
When using the +/-5V supply, the DA signal should be less than +4.3V.If it is stuck at 5V, check for a board short between pins 7 & 8. (DA and VCC+)The device schematic shows a base emitter (diode) drop then 360 ohms (60 + 300) when driving high. So DY(high)=VCC+ - 0.7V - Iout*360 ohms.
I see that this is old and may have been worked out but my 2 cents? I think all you need to do is turn on the local echo in Hyperterminal. In Hyper Terminal go to File - Properties. In Properties choose the Settings Tab and then the ASCII Setup button. In ASCII Setup check the box "echo typed character locally".
All content and materials on this site are provided "as is". TI and its respective suppliers and providers of content make no representations about the suitability of these materials for any purpose and disclaim all warranties and conditions with regard to these materials, including but not limited to all implied warranties and conditions of merchantability, fitness for a particular purpose, title and non-infringement of any third party intellectual property right. TI and its respective suppliers and providers of content make no representations about the suitability of these materials for any purpose and disclaim all warranties and conditions with respect to these materials. No license, either express or implied, by estoppel or otherwise, is granted by TI. Use of the information on this site may require a license from a third party, or a license from TI.
TI is a global semiconductor design and manufacturing company. Innovate with 100,000+ analog ICs andembedded processors, along with software, tools and the industry’s largest sales/support staff.