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A SIMPLE ADC ON AN LTC1286 CHIP

by Yuri Magda

Start ý The Software ý The Input Signal Handler and Interface ý Code Concerns ý The Design and Details ý Sources and PDF

THE INPUT SIGNAL HANDLER AND INTERFACE

The handling of an input signal is implemented through Ports 378h and 379h of the printer and is realized in function GetData. I used Delphiýs built-in assembler to write this function. The function returns the result as a real number in the variable resultData. Refer to Figure 2 as I explain how GetData works.

Figure 2ýThe LTC1286 operating sequence can be seen here.

The first thing you must do is initialize the LTC1286 chip. Itýs necessary to bring *CS high (1) for a short period (see lines 50ý57 of the program code in Listing 1). After that itýs possible to start conversion. The conversion is initiated on the falling edge of *CS and will require 14 clock cycles to complete. The serial data is transferred through Dout synchronously with the falling edge of the clock.

Note that the MSB (B11) is available after the falling edge of the third clock cycle, B10 after the fourth, and so on. The resultData will hold the result of conversion as the value:

B11 ý 2¹¹ + B10 ý 2¹⁰ + ý + B0 ý 2⁰

The conversion procedure is realized in lines 58ý77 of the program code in Listing 1.

After all is said and done, itýs necessary to multiply the resultData by 0.0012 (1.2/1000) and return a final result back to the basic program (lines 78ý79).

The interface part of the program is written using Delphi. I arranged four buttons, TButton, a one-line editor (TEdit), label (TLabel), and timer (TTimer), on the main application form (see Photo 2). The program code for the event handlers (buttons and timer) is shown in lines 82ý107 of the program code in Listing 1. Those of you who have experience with programming on Delphi can easily understand this piece of code.

Photo 2ýThis window shows the Delphi main application form. (Click to enlarge)

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