Connecting RC2014 to PC via MAX3232

[James Harland]

Hi everyone,

So in a way this is a continuation of our conversation about connecting to an AT&T terminal, but I want to make things easier and start by connecting to a Linux box via MAX3232. I have an old desktop computer which has a nine pin serial port, running Linux, and it turns out I already have a MAX3232 board, with five capacitors as Spencer said, though I've no idea of the quality - I think it was included in my Arduino starter set, at least that's where I found it.

So, looking at the MAX3232 board I see it has four pins: VCC, RXD, TXD, and GND. It does not have the RTS and CTS pins that the USB-C adapter which came with my RC-2014 uses.

So looking at the USB C adapter, RX is yellow, TX is orange, and 5V and GND are red and black respectively.

So If I connect the four corresponding pins of my RC2014 serial i/o to the MAX3232, and plug it into my PC, am I good to go? Obviously I'll need to set up things on my Linux box but I'm guessing that's no different really from doing it over USB, I'll just have to find the name of the device using dmesg.

I just want to check that this is safe before I plug in my RC-2014 and blow it up. I take the advice from the thread I mentioned that I need to check the quality of the part I have, and that the IC does not overheat.

Here is a picture of the board I have:

 

[Michelle Lawson]

Funny you should mention that. I have also been looking at some of those modules. Most seem to only have transmit & receive. I found one that also had RTS & CTS. So I started to dig through my stuff and found a couple of Sipex SP233ACP chips. It looks like Maxim also makes one as well, the MAX233 & MAX233A. I'm going to go that route so I can also insert a switch of sorts to change the DB9 end from DTE to DCE. 

Hmm, seems I can't post an image of the schematic. Odd......

[Peter Onion]

My "bodged up" solution :-)  The break-out board gives access to all four channels (2xRX, 2xTX).

PeterO

[Ed Silky]

A lot of terminal connections only used TX&RX (no handshake), using either XON/XOFF (soft handshake) or not worrying about handshake at all. In the case of your BBS example, the modem was most likely 1200 or maybe 2400 baud, so the system shouldn't have had a problem keeping up with that. For faster data sources being displayed on a terminal, you would occasionally see a 'hiccup' in the output. Some terminals would beep if their input buffer was overflowed (and therefore data was lost). If you had a slow terminal and a steady data stream at a higher baud rate (say 19,200 or maybe you had one that could use 38,400) you would find the terminal beeping at a fairly steady pace.

RS-232 communication at longer distances (100+ feet of cable) wasn't typically expected to be run faster than 9600, or maybe 19,200, baud. For higher speeds and/or longer distances a different interface was used (RS-422 or other differential circuits).

-Ed

--
You received this message because you are subscribed to the Google Groups "RC2014-Z80" group.
To unsubscribe from this group and stop receiving emails from it, send an email to rc2014-z80+...@googlegroups.com.
To view this discussion, visit https://groups.google.com/d/msgid/rc2014-z80/35a05299-9ee6-4443-aa37-2f799851f23bn%40googlegroups.com.

[Robb Bates]

I bought a few generic 232 type chip modules and hooked them up.  I realized eventually that while they were 5V tolerant, they had to be powered by 3.3V.  They get super hot and eventually die if powered by 5V.

Also, those series resistors can damp down the signal enough so that it doesn't get through.  I've bypassed mine on some of my setups.

Robb

[Michael Druckenmiller Sr]

For reference:

This is a better pic of my utilization of A MAX232. The signals to the left go directly to the MC68B50 Serial Port. The signals to the right go directly to a DB9 connector.

Attached is the Texas Instruments Data Sheet. Unfortunately they use the newer schematic symbols which, at least to me, are absolutely confusing.

If there is enough interest, I could put a 'tech page' on my web site where this stuff would be more easily indexed and found.

[Doug Jackson]

Ahhhh, yes....  The bizarre European IEEE 91 standard.

"Transforming simple schematics into glorious block diagrams no one asked for since 1984."

https://www.ti.com/lit/ml/sdyz001a/sdyz001a.pdf

Kindest regards,

Doug Jackson

em: do...@doughq.com

ph: 0414 986878

--
You received this message because you are subscribed to the Google Groups "RC2014-Z80" group.
To unsubscribe from this group and stop receiving emails from it, send an email to rc2014-z80+...@googlegroups.com.

To view this discussion, visit https://groups.google.com/d/msgid/rc2014-z80/7abe4259-4718-40b0-8d84-e3250ddceca9%40protonmail.com.

[Ed Silky]

The datasheet recommends a 5th capacitor close to the chip from VCC to GND. Also, the MAX323A uses 0.1uF caps, while the MAX232 uses 1.0uF.

Here is a link to the Maxim datasheet: https://www.analog.com/media/en/technical-documentation/data-sheets/max220-max249.pdf

-Ed

To view this discussion, visit https://groups.google.com/d/msgid/rc2014-z80/CAM_9E61KdrnScEvWCGWO2c64vPJtYfocPRE_2WqvM75e_UWYTg%40mail.gmail.com.

[Michael Druckenmiller Sr]

I suspect, though, that the performance with the 0.1uFd caps is not as good as with 1.0 uFd caps. See middle graph bottom of page 4. My board is using the TI chip at 115.200 Kbs. Sorry for any confusion I may have caused.

To view this discussion, visit https://groups.google.com/d/msgid/rc2014-z80/CACc-Qn%2B2XMY%3DXCukFNGnNpwwoagoEJUPH1837z0Br4Cj97i%3DzA%40mail.gmail.com.

[Ed Silky]

I agree that for the MAX232, the recommended value is 1.0uF. For the MAX232A, it is 0.1uF. I just wanted users of the chip to be aware that there is a difference in the recommendation. And the MAX220 uses different values from either of those (just in case people happen to use it).

-Ed

To view this discussion, visit https://groups.google.com/d/msgid/rc2014-z80/f0b7b8dd-45fc-4d4f-9878-0d9fa0516b37%40protonmail.com.