Use a PC's parallel port to program a clock source
Edited by Brad Thompson
By William Grill, Honeywell BRGA, Lenexa, KS -- EDN, December 7, 2004
This Design Idea shows how you can use Linear Technology's LTC6903 programmable oscillator as a clock source for direct-digital synthesis, data conversion, switched-capacitor filtering, clock, and voltage-controlled oscillator circuits. The LTC6903 operates from 2.7 to 5.5V with modest power consumption and can produce clock signals at frequencies of 1 kHz to 68 MHz. Typical frequency error and resolution over the range are 1.1 and 0.1%, respectively.
You can control the programmable oscillator circuit in Figure 1 via an IBM-compatible PC's parallel port, which also provides power to the circuit. Resistors R1 and R2 limit power-supply current drawn from parallel-port data bits DB3 and DB4, and resistors R3 through R5 isolate programming bits DB0 through DB2. A precision micropower voltage reference, IC1, provides 4.096V of stable power to IC1 and IC2. For optimal performance, minimize the lead lengths of bypass capacitors C1 and C2 with respect to IC2's power and ground connections. High-speed buffer IC3 isolates IC2's output and prevents frequency pulling due to load variations. Listing 1 translates a user-supplied input into a 16 bit, SPI-compatible data stream that programs IC1's output frequency. The LTC6903's output frequency depends on two control coefficients, OCT and DAC. The program derives the closest values for OCT and
DAC by solving the equation: f=(2OCT)×2078/(2–(DAC)/1024). At initial application of power, IC2's output frequency defaults to 1.039 kHz.
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How do I find the "Listing 1" for design idea "Use a PC's parallel port to program a clock source" by William Grill in December 7 EDN?
Curt Schubert - 2004-31-12 11:17:00 PST -
Re: Design Idea "Use a PC's parallel port to program a clock source" in the 12/7/2004 issue: Where is the listing that goes with this article?
Robert Penoyer - 2004-22-12 15:04:00 PST -
in reference to
< Use a PC's parallel port to program a clock source >
< By William Grill, Honeywell BRGA, Lenexa, KS -- EDN, 12/7/2004 >
The need to explain how to output/input data via PC's Parallel Printer Port or COM Series Port is missing!
How do to couple a BASIC program ( for example ) to the Port; is a subject that I have spent considerable time researching....without much success.
Many sites on the Internet deal with this question. NONE explain
what happens inside the computer, NONE explain the precise program used for both output/input to the PC.
A simple example of how to output/input data through the computer PORT to external electronics is sorely needed.
martin sehnven e-mail: hawkeye@netvision.net.il
martin sheven - 2004-8-12 03:26:00 PST
