Televideo 910

thanks Stephen , that will work with an 232 adapter for the Pi

I’m thinking that wednesday night will a good time to test the 910 On a pi… Are you willing to give it a go?

Sure.

Excellent , i will have the bits there

Like most of my ideas, someone (in this case, you guys :P) got to it two years before I did.

@crashman39 says we need to order a chip?

No, you need:

  1. USB to RS232 adapter - search AliExpress “USB rs232 adapter”
  2. 9 to 25 pin cable - I may have already made this up

If anyone needs a loaner USB/RS232 cable then I have one. I also have a DB9/25 adapter.
The cable exposes a female DB9 (DB25 with the adapter attached).

Anyone interested?

the thing is that the level maybe too high coming out on the televideo 910 , and in discussions with Stephen, we had to get a rs232 chip that will convert from 15v +_ to 3.3v for the uart pins on the pi …and directly drive anything from there … i have to find the discussion with Stephen to find the chip.

I am not clear here. I thought the pi will attach to the USB side and the tv910 to the RS232. If the TV910 expects 3.3v (unusual on a DB connector) then you need a USB/TTL cable/adapter. These are either 3.3v or 5v and some are voltage selectable.

Then again maybe I got the wrong end of the issue…

Gents, the tv910 port is standard rs232. That means +/- 12 volt levels.

@eyal is correct, an USB/rs232 adapter cable has the correct level drivers to match the rs232 standards.

@crashman39 is not talking about using the pi USB port, he is talking about using Pi gpio pins configured for uart operation. This will require a level shifter chip to interface the +/- 12 signals to 3.3 logic levels.

The MAX3232 chip is suitable.

We attached a USB/RS232 + DB9/25 to the TV910. Locally the 910 does not respond to keystrokes (no echo?). From the PC (putty) no reaction at all either. Based on the switches say 9600 baud.

Check your cables, I tested it 6 months back and it was fine. I believe the pin out is non-standard, plug is male, I.e. gendered for DTE but wired as DCE.

This is recorded in a post above.

Tested two cables. However, maybe a crossover cable is required? It will then not be the correct gender as a standard xo cable.
Better still, I have a special DB25 M/F adapter where the wiring between the two sides is jumpered rather than fixed. Should make this work.

@eyal, all the required information to get it working is contained in the first posting in this thread.

Getting some weird character echos I’m not sure how to resolve; but I’ve had success!

image

I’ll make sure I have my termcap settings correct tomorrow.

A shoddily built cable has done the job based on the specs that @sjdavies discovered and provided :slight_smile:

image

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Cool. First post has a link to the tv910 reference manual. This may help you configure the termcaps.

I ended up opening the terminal and giving it a semi-decent clean with compressed air, and isopropyl.

image image image image image

And this afternoon I made a nicer cable mostly because I somehow ripped a pad off my frankencable and couldn’t fix it.

@sjdavies, noob serial terminal question: is the four pins enough? It certainly mostly works with only the four pins. (Wondering where the weird extra characters might be coming from).

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After fixing the pinout mistakes I had made with my new cable, all is working! and the weird extra characters have gone - I suspect it was a short or something with my previous frankencable, and not the keyboard having been cleaned now that has fixed it.

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and here is the result of Jamie and the rest of us here on this thread
thanks for helping and doing a great job 20200104_135746 20200104_141521 20200104_144524 20200104_145312

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Possibly some noise on the tx/rx signals. UARTs are very noise sensitive.

Sounds like you’ve hacked up a great solution :+1:

The quick answer to your noob question is that 3 or 5 wires are sufficient. You can either:

  1. tx/rx, rx/tx, gnd/gnd - minimal but requires xon/xoff flow control
  2. tx/rx, rx/tx, gnd/gnd, rts/cts, cts/rts - hardware flow control.

The longer answer to understanding RS232 requires that you understand equipment roles, there are two. Data Terminal Equipment (DTE) and Data Communication Equipment (DCE). Dumb terminals, PCs and routers are generally setup as DTE. Modems, leased lines, xDSL modems are regarded as DCE.

As a general rule the DTE will be fitted with a plug, the DCE is fitted with a socket. A further complication is that the pinout changes depending on DTE v DCE. The concept is that DTE and DCE can be connected using a straight/flat cable i.e. pin 1 -> 1, 2 -> 2 … 25 -> 25
For this to work correctly output pins on the DTE side need to align with input pins on the DCE side. This can make RS232 connections VERY confusing. Also, not all manufacturers produced equipment matching the standard.

Key Pins for 25 pin RS232 (DTE)
1 - frame ground (NB. shield wire in cable, soldered to connector frame)
2 - TxD (O)
3 - RxD (I)
4 - RTS (O)
5 - CTS (I)
6 - DSR (I)
7 - signal ground (NB. isolated from frame ground, pin 7 only)
8 - CD (I)
20 - DTR (O)
22 - RI (I)

Key Pins for 25 pin RS232 (DCE)
1 - frame ground (NB. shield wire in cable, soldered to connector frame)
2 - RxD (I)
3 - TxD (O)
4 - CTS (I)
5 - RTS (O)
6 - DSR (O)
7 - signal ground (NB. isolated from frame ground, pin 7 only)
8 - CD (O)
20 - DTR (I)
22 - RI (O)

Note that the DCE side has more outputs and the DTE has more inputs.

Modem Controls

Dataset Ready (DSR) indicates the modem is ready i.e. modem power is on.
Ring Indicator (RI) is used in dialup modems to indicate an incoming call i.e. phone is ringing.
Data Terminal Ready (DTR) means the DTE side is good to go. This is normally asserted when the terminal software opens the serial port.
Carrier Detect (CD) gets asserted by the modem after connection has been made to the outside world and an agreed protocol has been negotiated e.g. 28800 baud.

None of the modem control signals are required for serial port operations.

From memory, the TV910 has configurable switches that determine flow control and which of the RS232 signals it bothers paying attention to.

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