EXPERIMENT 8
INTERFACING ADC AND DAC
ADC0804 Chip
The ADC0804 IC is an 8-bit parallel ADC in the family of the ADC0800 series from National Semiconductor. It is also available from many other manufacturers. It works with +5 volts and has a resolution of 8 bits. In the ADC0804, the conversion time varies depending on the clocking signals applied to the CLK IN pin, but it cannot be faster than 110µs. The following is the ADC0804 pin description.
* CS
Chip select is an active low input used to activate the ADC0804 chip. To access the ADC0804, this pin must be low.
* RD (read)
This is an input signal and is active low. The ADC converts the analog input to its binary equivalent and holds it in an internal register. RD is used to get the converted data out of the ADC0804 chip. When CS = 0, if a high-to-low pulse is applied to the RD pin, the 8-bit digital output shows up at the D0-D7 data pins. The RD pin is also referred to as output enable (OE).
WR (write; a better name might be “start conversion”)
This is an active low input used to inform the ADC0804 to start the conversion process. If CS = 0 when WR makes a low-to-high transition, the ADC0804 starts converting the analog input value of Vin to an 8-bit digital number. The amount of time it takes to convert varies depending on the CLK IN and CLK R values explained below. When the data conversion is complete, the INTR pin is forced low by the ADC0804.
* CLK IN and CLK R
CLK IN is an input pin connected to an external clock source when an external clock is used for timing. However, the 804 has an internal clock generator. To use the internal clock generator (also called self-clocking) of the ADC0804, the CLK IN and CLK R pins are connected to a capacitor and a resistor, as shown in Figure 13-1. In that case the clock frequency is determined by the equation:
f= 11.1RC
Typical values are R = 10K ohms and C = 150 pF. Substituting in the above equation, we get f = 606 kHz. In that...