Touchscreen Interface - Micros Systems Workstation 4 LX Service Manual

WS4 Technical Overview

Touchscreen Interface

Touchscreen Interface

REF: AB28/ABRD36 - Sheet 7
The touchscreen interface supports a 5-wire resistive touchscreen and is located on
Sheet 7 of the Schematic. The touchscreen controller output is connected to COM2.
UART1 in the SC3200 is dedicated to this interface.
The interface consists of touchscreen controller U38, microcontroller U37 and serial
EEPROM U40.
U38 is a Burr-Brown (part of Texas Instruments) ADS7845E 12-bit sampling
analog-to-digital converter (ADC) with a serial interface.
The ADS7845E is coupled to U37, a P87C52 8-bit micro controller that contains the
firmware to initiate the analog-to-digital conversion process and convert the output
into ASCII serial data.
U37 supplies a clock to the
serial control byte to the
begin the conversion, it enters the acquisition mode. When the control byte is
complete, the ADC enters the conversion mode where the actual analog-to-digital
conversion takes place. The ADS7845E sends output data in straight binary format to
the micro controller. U37 converts the binary data to ASCII serial data which appears
on the TOUCHSCREEN_TX
to UART1 in the SC3200 processor.
Serial EEPROM U40 is attached to the micro controller and stores calibration values
as well as communications parameters for the interface.
2-20
input and starts the conversion process by writing a
DCLK
DIN of the ADC. When the ADC has enough information to
and TOUCHSCREEN_RX
Workstation 4 and 4 LX Field Service Guide
pins. These pins are connected