Question: PSR-500/600 PC/IF interface specifics.

[smokeyjones666]

I'm wondering if anybody out there has any information regarding the specifics of the PC/IF port. Does the port use all three pins or just two? Which ones are TX and RX, or is it much more complicated than that? Is it a TTL interface and if I want to talk to it with a hardware device am I going to need some 'glue logic' to tie the whole thing together?

Basically, anything on the specs and how to interface with it on the hardware side - without using the GRE/RS USB cable - is what I'm looking for. If anybody out there has any info they can share, I'd be very appreciative.

Thanks,
Ryan.

[smokeyjones666]

Okay, since I haven't received a response yet I decided to try to figure out what I can about the RS/GRE USB programming cable. This is what I've learned:

The device is based on the FTDI FT232BL USB UART IC. (Data sheet: http://www.ftdichip.com/Documents/Da...DS_FT232BL.pdf )
Pin 24, RXD, is tied to Tip on the 1/8" plug through a 100 ohm resistor.
Pin 25, TXD, is tied to the Middle on the 1/8" plug, also through a 100 ohm resistor.
Ring on the 1/8" plug is tied to ground.
Pin 13, VCCIO, appears to be tied to pin 6, 3V3OUT (there is no resistance between the two pins).
When I measure the voltage between the Tip to the Ring I get 3.51v, voltage from the Middle to the Ring is 3.54v (at least, according to the limitations of my multimeter.) I would have expected zero, since I'm not transmitting or receiving, but this is all over my head anyway or I wouldn't be asking, right?

From the FTDI data sheet about Pin 13, VCCIO:

+3.0 volt to +5.25 volt VCC to the UART interface pins 10..12, 14..16
and 18..25. When interfacing with 3.3V external logic in a bus powered
design connect VCCIO to a 3.3V supply generated from the USB bus. When
interfacing with 3.3V external logic in a self powered design connect VCCIO
to the 3.3V supply of the external logic. Otherwise connect to VCC to drive
out at 5V CMOS level.

From the reference for my Arduino Duemilanove (Arduino - ArduinoBoardDuemilanove)

Each of the 14 digital pins ... can be used as an input or output... They
operate at 5 volts. Each pin can provide or receive a maximum of 40 mA and
has an internal pull-up resistor (disconnected by default) of 20-50 kOhms...

also

Serial: 0 (RX) and 1 (TX). Used to receive (RX) and transmit (TX) TTL
serial data. These pins are connected to the corresponding pins of the FTDI
USB-to-TTL Serial chip.

Here's where I'm hoping I can get the attention of someone smarter than I. I gather from what I've learned here, the part that plugs into the radio is using 3.3 volt logic. According to the reference for my Arduino board, the built-in serial interface pins are 5 volt. I'm assuming I'm going to have to reduce this to 3.3 volts somehow. Is there a simple way to do this, a pulldown resistor perhaps?

Also, does anybody have enough experience with this to tell me if I'm going to fry my radio going about this in this particular way and is there any advice on what I can do to avoid that? (I mean, besides just leaving well-enough alone. )

[tonycash]

Ryan,
After seeing your message I just had to try my ADMS serial cable on my GRE PSR-600.
I really expected it to work but when I told PSRedit500 to download the scanner, it did
trigger the scanner to output it's memory but the data was never received by the program.
And when I tried to upload to the scanner the scanner and the scanner came up with the
PC/IF something screen and said polling sender but nothing else ever happens. So it seems
to me the txd from the computer to scanner is working but not the rxd, go figure. Good luck
with getting it to work, I would love to hear what you did IF you do get it to work.

73 de Tony, KD4K

[Eng74]

I know one thing that is different from the other GRE/RS scanners (92/93/95/96) is that you need a stereo cable to clone the 500/600 radios. I have 3 of the clone cables that came with the 92/2067's and they didn't work had to get a cable (42-2497 for those keeping track) from RS.

[wayne_h]

My advice and from a cable DIY'er is to buy the GRE cable. The FTDI USB to bare cable ends is 20-ish bucks. I'd say for a plug and labor you're about equal to the cost of a brand new GRE cable.

I learned the hard way when building a SiriusConnect cable. Could have bought a premade one for less after the research and errors I made making one.

Also, the newer models use all three pins. The older models like the PRO-96 use two. You would use the 5v version and not the 3.3v IIRC. The FTDI USB cable comes in handy for various projects when the programming cables are stupidly priced.

[smokeyjones666]

Originally Posted by wayne_h

My advice and from a cable DIY'er is to buy the GRE cable. The FTDI USB to bare cable ends is 20-ish bucks. I'd say for a plug and labor you're about equal to the cost of a brand new GRE cable.

I learned the hard way when building a SiriusConnect cable. Could have bought a premade one for less after the research and errors I made making one.

Also, the newer models use all three pins. The older models like the PRO-96 use two. You would use the 5v version and not the 3.3v IIRC. The FTDI USB cable comes in handy for various projects when the programming cables are stupidly priced.

Actually, you may have just helped me, but not from your suggestion that I should buy the GRE data cable (I already have two of them.) I'm looking to use my Arduino board to send control commands to the PSR-500 and if I can indeed use 5v without frying the PC/IF port, I believe I can interface directly with the scanner without having to resort to using any 'glue logic'. This would be a big win, because I can use stuff I already have to test this.

[pro92b]

The schematic below is from the PRO-96 but I expect that the PSR-500 has some similar characteristics. The supply voltage for the CPU in the PRO-96 is 3.5V. For the PSR-500 it will be the same or lower. Nobody builds CPU's that run on 5V anymore. The two Schottky clamp diodes in the PRO-96 are very likely used in the PSR-500 too. In the PRO-96 the CPU has two pins connected to the PC/IF circuit. In the PSR-500 those two pins are probably connected individually so the communication is full duplex.

If you connect a 5V source to the PC/IF jack, D203 will try to clamp it to the 3.5V power bus. If the 5V supply is low impedance it may destroy the diode and ultimately the CPU. There are 3.3V logic gates available that are 5V input tolerant and I'd strongly recommend that you use one to interface to the scanner.

[smokeyjones666]

Originally Posted by pro92b

If the 5V supply is low impedance it may destroy the diode and ultimately the CPU.

Would something like this be the reason for the 100 ohm resistors on the RXD and TXD lines from the FTDI chip, to protect the scanner from something bad happening on the programming cable side?

[smokeyjones666]

Ok, I've been doing a little reading and it seems there are a few different ways to convert between the two voltages, but I think I like the approach pro92b is suggesting with the logic gates.

There seems to be quite a variety of them, but the 4050 (4000 series CMOS Logic ICs) appeals to me somehow. I was thinking two of these, one powered at 3.3v for the Arduino TX line and one powered at 5v for the Arduino RX line, with 100 ohm current limiting resistors on the inputs and outputs.

Am I going in the right direction with this and will this older chip design be able to handle the 115200bps data rate required by the scanner?

[kevins669]

Originally Posted by pro92b

The schematic below is from the PRO-96 but I expect that the PSR-500 has some similar characteristics. The supply voltage for the CPU in the PRO-96 is 3.5V. For the PSR-500 it will be the same or lower. Nobody builds CPU's that run on 5V anymore. The two Schottky clamp diodes in the PRO-96 are very likely used in the PSR-500 too. In the PRO-96 the CPU has two pins connected to the PC/IF circuit. In the PSR-500 those two pins are probably connected individually so the communication is full duplex.

If you connect a 5V source to the PC/IF jack, D203 will try to clamp it to the 3.5V power bus. If the 5V supply is low impedance it may destroy the diode and ultimately the CPU. There are 3.3V logic gates available that are 5V input tolerant and I'd strongly recommend that you use one to interface to the scanner.

...PC/IF from PSR-500/PRO-106

-- Kevin