ICL7109 pdf datasheet (12-Bit,

The ICL7109 is a high performance, CMOS, low power
integrating A/D converter designed to easily interface with
microprocessors.
The output data (12 bits, polarity and over-range) may be
directly accessed under control of two byte enable inputs and a
chip select input for a single parallel bus interface. A UART
handshake mode is provided to allow the ICL7109 to work with
industry-standard UARTs in providing serial data transmission.
The RUN/HOLD input and STATUS output allow monitoring
and control of conversion timing.
The ICL7109 provides the user with the high accuracy, low
noise, low drift versatility and economy of the dual-slope
integrating A/D converter. Features like true differential input
and reference, drift of less than 1μV/oC, maximum input bias
current of 10pA, and typical power consumption of 20mW
make the ICL7109 an attractive per-channel alternative to
analog multiplexing for many data acquisition applications.