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Spartan-3A/3AN FPGA Starter Kit Board User Guide
UG334 (v1.1) June 19, 2008
Chapter 5:
Character LCD Screen
R
Character LCD Interface Signals
Table 5-1
shows the interface character LCD interface signals.
Voltage Compatibility
The character LCD is power by +5V. The FPGA I/O signals are powered by 3.3V. However,
the FPGA’s output levels are recognized as valid Low or High logic levels by the LCD. The
LCD controller accepts 5V TTL signal levels and the 3.3V LVCMOS outputs provided by
the FPGA meet the 5V TTL voltage level requirements.
The 390
Ω
series resistors on the data lines prevent overstressing on the FPGA and
StrataFlash I/O pins when the character LCD drives a High logic value. The character LCD
drives the data lines when LCD_RW is High. Most applications treat the LCD as a write-
only peripheral and never read from the display.
UCF Location Constraints
Figure 5-2
provides the UCF constraints for the Character LCD, including the I/O pin
assignment and the I/O standard used.
Table 5-1:
Character LCD Interface
Signal Name
FPGA Pin
Function
LCD_DB<7>
Y15
Data bit DB7
LCD_DB<6>
AB16
Data bit DB6
LCD_DB<5>
Y16
Data bit DB5
LCD_DB<4>
AA12
Data bit DB4
LCD_DB<3>
AB12
Data bit DB3
When using the four-bit
interface, drive these signals
High.
LCD_DB<2>
AB17
Data bit DB2
LCD_DB<1>
AB18
Data bit DB1
LCD_DB<0>
Y13
Data bit DB0
LCD_E
AB4
Read/Write Enable Pulse
0: Disabled
1: Read/Write operation enabled
LCD_RS
Y14
Register Select
0: Instruction register during write operations.
Busy Flash during read operations
1: Data for read or write operations
LCD_RW
W13
Read/Write Control
0: Write, LCD accepts data
1: Read, LCD presents data
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