ADC0809 is an 8-channel, 8-bit successive approximation A/D analog-to-digital converter produced by National Semiconductor Corporation. There is an 8-channel multi-channel switch inside, which can latch the decoded signal according to the address code, and only one of the 8 analog input signals can be selected for A/D conversion. It has been phased out.
Key features:
1) 8 input channels, 8-bit A/D converter, that is, the resolution is 8 bits.
2) It has a conversion start-stop control terminal.
3) Conversion time of 100μs (when clocked at 640kHz), 130μs (when clocked at 500kHz)
4) Single +5V power supply
5) Analog input voltage range 0~+5V, no zero point and full scale calibration required.
6) The operating temperature range is -40~+85 degrees Celsius
7) Low power consumption, about 15mW.
Internal structure
ADC0809 is a CMOS monolithic successive approximation A/D converter, the internal structure is as shown in the figure, it is composed of 8 analog switches, address latches and decoders, comparators, 8-bit switch tree A/D converters, successive approximation registers, logic control and timing circuits.
External Features (Pin Functions)
ADC0809 chip has 28 pins and is available in a dual in-line package, as shown in the figure. The functions of each pin are described below.
IN0~IN7: 8 analog inputs.
2-1~2-8: 8-digit digital output.
ADDA, ADDB, ADDC: 3-bit address input line for strobe one of the 8 analog inputs
ALE: Address latching allows signals, inputs, high levels are valid.
START: A/D conversion starts the pulse input, inputs a positive pulse (at least 100ns wide) to start it (the rising edge of the pulse resets 0809, and the falling edge starts A/D conversion).
EOC: A/D conversion end signal, output, when A/D conversion ends, this end outputs a high level (low level during the transition).
OE: Data output allows signal, input, high level valid. When the A/D conversion is over, a high level is input at this end to open the output three-state gate and output the digital quantity.
CLK: Clock pulse input. The clock frequency is required to be no higher than 640KHZ.
REF(+), REF(-): Reference voltage.
Vcc: Power supply, single +5V.
GND: Ground.
The working process of editing this section first enters a 3-bit address, and makes ALE=1 to store the address in the address latch. This address is decoded and strobe one of the 8 analog inputs to the comparator. The START rising edge will gradually approximate the register reset. The A/D conversion is started along the drop edge, after which the EOC output signal becomes low, indicating that the conversion is in progress. Until the A/D conversion is complete, the EOC becomes high, indicating that the A/D conversion is over, and the resulting data is stored in the latch, which can be used as an interrupt request. When the OE input is high, the output three-state gate opens, and the digital amount of the conversion result is output to the data bus.
Transmission of converted data The data obtained after A/D conversion should be transmitted to the microcontroller for processing in time. The key issue in data transfer is how to confirm the completion of the A/D conversion, because only after the confirmation is completed, can the transmission be carried out. The following three methods can be used to achieve this.
(1) Timed transmission method
For an A/D converter, the conversion time is known and fixed as a technical indicator. For example ADC0809 conversion time is 128μs, which is equivalent to a total of 64 machine cycles for the MCS-51 microcontroller at 6MHz. A delay subprogram can be designed accordingly, and this subprogram will be called after the A/D conversion starts, and when the delay time arrives, the conversion must have been completed, and then the data can be transmitted.
(2) Inquiry method
The A/D conversion chip consists of a status signal indicating that the conversion is complete, such as the EOC side of the ADC0809. Therefore, you can use a query method to test the status of EOC, confirm whether the conversion is complete, and then transfer the data.
(3) Interruption method
The status signal (EOC) indicating that the conversion is completed is used as an interrupt request signal and the data is transmitted in an interrupt manner.
Regardless of which method is used, once the conversion is complete, data can be transmitted via instructions. When the export address is sent first and the signal is valid, the OE signal is valid, and the conversion data is sent to the data bus for the microcontroller to accept. //www.chip100.com/