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PIC16x84 programmer

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Last Update on:27/7/99

There was a 470kOhm resistor shown in the previous schemtaic. This is wrong it should be around 1k. I have fixed the schematic. Now there is only one .HEX file to download, it works on both the PIC16C84 and the PIC16F84 (the old one for the PIC16F84 had a bug).

I have received many positive email saying that the link works perfectly.

In the new version of TI's Graphlink Software, TI has introduced support for the old Black link which is compatible with the '$4 Serial Link'.  So it might seems as if the PICLink isn't of any use anymore, but this is not true. It is still the only homemade link of Macintosh (althoug nobody has tested it with a MAC)  and can be used to connect the calc to a modem.

Here you can find everything you need to build the PICLink. The PICLink enables data transfers between computers (PCs and MACs) and calculators from TI (TI7x, TI8x, TI9x...). This device is intended to be 100% compatible with the GrapLink from TI. Thus the GraphLink Software provided by TI can be used with this link. 

This device converts between the protocol used by the calc and the RS232 one used by the computer. The calc sends and receives bytes in a special protocol using its 2 open-drain lines. The computers tranfers bytes using the serial protocl at 9600 bps, 8-Bit no parity and no handschaking. 

The advantage of this link over the other homemade links (i.e. the "$5 parallel" and "$4 serial" links ) are: 

  • Availability of software for newers calcs.
  • Can be used with MACs.
  • Can be used to connect the calc to a modem.

The disadvantage over the other homemade links is the relative high price, compared to $4. But still the PICLink is much cheaper than the real GraphLink from TI. 

This links is also somewhat slower than the other links. I was amazed to find that WTran8x was faster to use ( personaly I find it much easier to use my software than TI's one). 

The Tests: 

I have only tested the link between my 486 Notebook and my TI89 and it works fine with the GraphLink software from TI.
I have got also more than 30 responses saying that the link is working.
If you build one then please drop me a mail and tell me if it works or not. 

The Circuit: 

The circuit is very simple and only a small number of parts is used: The PIC, the resonator, 7 diodes, 6 resistors and a capacitor. The device takes its power from the serial port (RTS and DTR pins), so there is no need for an external power supply. 

The circuit use a cheap way to make the signal convertion between RS-232 level and TTL level, so cables must be short. The best way is to connect the device directly to the COM port. 

The pin-arrangments of the diodes and the LED is similar to that of the IR Link, so in order test it on an IR Link board you have just to add 3 wires that will be connected with the computer, and still use the IR Link power source. 

And here is the software for the PIC16C84 or PIC16F84: Piclink_old.hex
When programming make sure you set the fueses to: 


I began this project a long time ago but then I stopped because I encoutered some problems. The problem was that the computer was sending the data too fast: The computer sends the next byte when the PIC has not finished sending the previous byte to the calc. I did not find a way to solve this problem, so I just forgot the project. 

Some days ago I was looking again at the design and I have found a way to eleminate a wasted time of 100us (aprox. 1 bit time at 9600 bps). I tested the link again with a small program I wrote that output serial data fast, but it did not work properly. 

I tried then to use TI's software, and I was amazed to see it working and transfering variables! 

Future consideration: 

Soon I will make a PCB for it. I will also sells preprogrammed PICS with the software already on them for those who don't have a PIC programmer. I will try also to sell complete kits for the link (like the ones for the IR Link). I do not know the price of those kits but it should be around 11UKP (=$18) which is much less than the price of the GraphLink from TI. 

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Author : Sami Khawam