Using Lcd Port As Digital I/O - Technologic Systems TS-5700 User Manual

TS-5700 User's Manual

6.2 Using LCD Port as Digital I/O

The LCD Port can be used as 11 additional digital I/O lines or it can be used to interface
to a standard alphanumeric LCD display. At system reset, the port defaults to DIO
mode. If using an LCD display this port can be switched to LCD mode by writing a "1"
into bit 4 at I/O location Hex 7D, or the BIOS call to enable the LCD also sets bit 4 at I/O
location Hex 7D (See Section 8 for LCD mode).
When the LCD port is in DIO mode, pins LCD_RS and LCD_WR are digital inputs,
LCD_EN is a digital output, and LCD_0 thru LCD_7 are programmable as either inputs
or outputs.
LCD_RS and LCD_WR can be read at I/O location 73h bits 7 and 6, respectively. The
state of LCD_EN is controlled by writing to I/O location 73h bit 0.
LCD_0 thru LCD_7 can be read or written at I/O location 72h. The direction of this byte-
wide port (pins 7 – 14) is determined by bits 2 and 3 at I/O location 7Dh. If bit 2 is a zero, then the lower 4 bits
(pins 7 – 10) are inputs. If bit 2 is logic 1, then pins 7 – 10 are outputs. Bit 3 at location 7Dh controls the upper 4
bits, pins 11 – 14 in a like manner.
All digital outputs on this port can source 4 mA or sink 8 mA and have logic swings between 3.3V and ground.
The digital inputs have standard TTL level thresholds and must not be driven below 0 Volts or above 5.0 Volts.
The 5V power has a 750 mA Poly-Fuse to limit the current.
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Table 6.2 Pinout for LCD
header when used as DIO
LCD_6 14 13 LCD_7
LCD_4 12 11 LCD_5
LCD_2 10 9 LCD_3
LCD_0 8 7 LCD_1
LCD_WR 6 5 LCD_EN
Bias 4 3 LCD_RS
GND 2 1 5V
5/2009