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Forum Index : Microcontroller and PC projects : ASCII Video Terminal Issue
| Author | Message | ||||
| Grassy Newbie  Joined: 06/07/2014 Location: AustraliaPosts: 12 |
I have just finished building Geoff's ASCII Video Terminal but I have a strange problem that hopefully someone can help me with. At first I thought that it was working perfectly as I had success with a VGA monitor, keyboard, USB etc. all connected and sending & receiving serial data all ok. Then I tried it as just a USB serial converter without any screen connected and sending / receiving to and from a Micromite. I noticed that the characters were occasionally getting corrupted. Reconnecting the VGA monitor and rebooting fixed the problem so I decided to check the composite output and there is none. I should mention at this stage that I built this on prototyping board and did not use the PCB so there is every possibility that I have a wiring error but... I have disconnected pin 6 of the PIC and checked the signal on a CRO and there isn't anything at all. The sync pulses are present on pins 25 & 18 ok. So my question before I start a major re-soldering exercise is who has this working correctly with the composite output enabled. NB I have tried two PIC chips just in case one was faulty. When I programmed them I get a message saying something about a debug file being deleted. Many thanks for any assistance. |
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| cosmic frog Senior Member  Joined: 09/02/2012 Location: United KingdomPosts: 300 |
Hi, I have also just last week built Geoff's ASCII Video terminal on a piece of stripboard and have the same problem of no picture on the composite output, that is until I put it into NTSC mode using SHIFT F12, I then get a picture, although it seems a little unusable as you don't seem to have much space on screen and it doesn't fit properly, but there is a nice stable picture. I get nothing (black screen) in PAL mode. Apart from that everything else seems to work great! (I haven't tried the USB part yet). Dave. |
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| WhiteWizzard Guru  Joined: 05/04/2013 Location: United KingdomPosts: 2927 |
Grassy, You are probably aware of the following if you are following Geoff's series in the SC Magazine, but just in case not then note the following: At power-up, the Terminal will check for a connected VGA monitor. If found, then output is to vga only; if monitor not connected then output switches to composite. If you subsequently switch monitor types then no output will be observed as you need to reset the terminal to switch display output. ALSO do NOT connect composite AND VGA simultaneously. Regarding your characters occasionally getting corrupted can you please give a little more detail. What baud rate? Did you only have the problem when no initial display connected (i.e. when terminal will default to composite output). I will see if my TV/amp combo has a composite input and if so will try later tonight when the kids are in bed. I have several Terminals to try it on (Geoff's PCB x 2, and my own custom terminal - nicknamed TermMite-VT100). I will update you later in about 8 hours with progress BUT do let me know more detail of your setup parameters when you observe your 'issue'. Regards, WW |
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| Grassy Newbie Joined: 06/07/2014 Location: AustraliaPosts: 12 |
Thanks Dave, I am at work at the moment and cannot try your suggestion but I will try again tonight. At least there does seem to be some issue. |
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| Grassy Newbie Joined: 06/07/2014 Location: AustraliaPosts: 12 |
Sorry I should have been a bit clearer. I initially powered up the first time with a VGA monitor connected and everything worked perfectly. I did not have the composite monitor connected at that stage. I set the baud rate to 38400 using the setup screen and connected a uMite to the serial ports and was able to communicate perfectly. Then I connected a laptop to the USB ports, loaded the driver and with Teraterm was also able to communicate to the uMite. No problem with speed or any missing characters. Also everything I typed on the terminal keyboard was echoed correctly on the laptop and everything typed into Teraterm echoed to the VGA monitor. Next I powered down the Video Terminal and removed the VGA monitor to test in USB mode only. I did read the SC article so I was assuming the Terminal would default to composite mode but at this stage I did not have any monitor connected. I started Teraterm and pressed return a few times expecting to see the uMite prompt but all I got was either nothing or some incorrect characters. Holding the return key down I occasionally got the > prompt but typing in any command just resulted in missed or incorrect characters. It was at this stage I thought (as it should have now been in composite mode)I would try connecting a composite monitor. That's when I found it had no output. The VGA monitor was definitely disconnected. As a matter of interest I powered down again and connected a 1k resistor between pins 2 & 5 of the VGA connector to simulate a monitor and re-established the USB to uMite connection and everything worked perfectly again. Next I removed the resistor, rebooted and the dropped characters returned. I am using the firmware from the Silicon Chip site. I look forward to hear how you go with your composite monitor connected. Tony. |
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| Grassy Newbie Joined: 06/07/2014 Location: AustraliaPosts: 12 |
For anyone else building this I can confirm Dave's observation that you need to set the composite output to NTSC. The default PAL mode does not work and there is also a problem with serial to USB communications in this mode. When NTSC was selected I disconnected both monitors and was able to communicate with the uMite at 38400 via USB with no problems at all. This is a good work around for now. Many thanks. |
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Geoffg Guru Joined: 06/06/2011 Location: AustraliaPosts: 3269 |
Thanks Grassy, this is an annoying bug indeed. I have just got back to my work bench and I will investigate ASAP and hopefully come out with a fix in a few days. In the meantime the workarounds listed above seem to work. BTW, I have collected a few minor bug/issues with the Micromite but I will not have time to fix them before I set off on my next trip so they will have to wait until late August. Geoff Geoff Graham - http://geoffg.net |
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| Grassy Newbie Joined: 06/07/2014 Location: AustraliaPosts: 12 |
No worries Geoff it's still a brilliant little device and has already come in very handy for field programming. Cheers. |
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| robert.rozee Guru Joined: 31/12/2012 Location: New ZealandPosts: 2400 |
any chance of just a quickly recompiled version for the MX170 with just the ram size expanded upon? microchip were nice enough to send me a few samples, and it would be good to exercise them. cheers, rob :-) |
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| Geoffg Guru Joined: 06/06/2011 Location: AustraliaPosts: 3269 |
Sorry Rob, I am very short of time and I really don't want to released anything "half baked". Geoff Graham - http://geoffg.net |
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