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9957Re: [cosmacelf] Re: Seven Segment Displays

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  • Rick Cortese
    Apr 5, 2012
      Forewarning: Been over 30 years since I last did something original with an 1802. As Lee points out, you really need a data sheet to make sure how your LCD operate. The pinouts on the interfaces come in a couple of  flavors, 14 pin, or 2x7 pins are the most common and I think somewhat standard. The the Jameco have 16 pins with the additional pins for the backlight.

      If I was to try hooking one up: 

      I would tie the data lines 1:1 with the 1802. 

      I would tie the R/W low to keep it in write mode. They do have a ~64 bytes of RAM on them for redefined characters but I don't really think it would be necessary to access it in read/write mode. Ditto for the display memory, you can retrieve what is written to it but 2X16 is not enough memory to bother with. 

      The register select pin I would think about tying to the 1802 address line MA0 or just use Q to be safe. I forgot what happens to memory address lines during and OUTPUT instruction. <DOH!> If they stay the same for the output cycle you could just read from memory location XXXXXXX0 and XXXXXXX1 to set the LCD register select pins then follow with the OUTPUT 1<for instance> 1802 instruction. Q line is much easier, just set it for operation and be sure. As Lee said, since they have the 4 bit mode you probably could use one of the data lines for register select line but you may need a delay for the 4 bits for set up time.

      The LCD enable pin I would tie to one of the N0-N2 outputs of the 1802. I think its operation is inverted from what we have with the 1802. That is it would have to be run through a 4049 or something to get the polarity right. Back in the day I routed mine though a 74LS138 so I could have 8 output devices. IIRC a 74ls138 has inverted outputs so it could replace the 4049 and give you up to 8 I/O chips/devices. Of course you would want to use something like a 74C138 or 74HTC138 to keep with the low power theme.

      In use you would just 
      set Q level for command byte, OUTPUT1 command byte 
      set Q level data byte, OUTPUT1 data.

      I've probably committed some grievous oversight in how I would do it. IMHO, it would be a cute hack.


      ________________________________
      From: Kent Andersen <sci@...>
      To: cosmacelf@yahoogroups.com
      Sent: Wednesday, April 4, 2012 9:20 PM
      Subject: Re: [cosmacelf] Re: Seven Segment Displays


       
      how do you use displays like that? I have a pile of those types of
      displays that I use with arduino (Atmega) but I have never seen anyone
      interface one of these puppies to a 1802.

      On 4/3/2012 5:31 PM, eight_bit_jdrose wrote:
      >
      >
      >
      > --- In cosmacelf@yahoogroups.com <mailto:cosmacelf%40yahoogroups.com>,
      > Lee Hart <leeahart@...> wrote:
      > >
      >
      > > > I have used the 2X16 character displays like
      > > >
      > http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_2118580_-1
      > >
      >
      > Mr. Hart,
      >
      > That is a nice, contrasty display at a decent price.
      >
      > Do you know if there is a version of this display that is serial instead?
      >
      >

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