Digilent PmodCLP Reference Manual

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Revision: April 28, 2008

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Overview

The PmodCLP is a 16x2 character LCD module that
uses two Pmod connectors to present a 3.3V, 8-bit
parallel data interface to system boards. It is based on
a Sunlike LCD panel that uses a Samsung KS0066 (or
equivalent) LCD controller. The module can be
attached to any number of Digilent system boards to
create a character LCD subsystem.

The PmodCLP can be supplied with 3.3V or 5V.
Because the Sunlike LCD module requires a 5V
supply, the PmodCLP includes a 3.3V-to-5V boost
regulator and a 5V-to-3.3V voltage-translation circuit.
The voltage translation circuit ensures that 3.3V data
signals are returned to the system board whether 3.3V
or 5V is used to supply the module (if 5V signal levels
are desired, the 2.5V regulator can be
removed).

A simple resistor-divider contrast-setting circuit
is used to set the contrast voltage (VO) to
about 200mV, ideal for temperatures around
20C. The divider circuit values can be
changed to define other contrast voltage
settings.

The module is capable of displaying any one
of more than 200 predefined characters in
each of the 32 display locations (organized as
16 characters on two rows). Most characters
use ASCII codes (see the Samsung KS0066
data sheet for a complete list of character
codes). The module can also execute a variety
of instructions, such as erasing specific characters, setting different display modes, scrolling, and
displaying user-defined characters. These instructions are defined in table 3 below. Characters and
instructions are written to the display using the 8-bit data bus as described below. Characters written
to the display appear at the current location of the LCD panel’s cursor.

This document contains much of the information required to drive the PmodCLP, but a good deal of
the information presented in the LCD controller data sheet has not been reproduced here. Please
refer to the Samsung manufacturer’s data sheet for more information.

PmodCLP Block Diagram

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PmodCLP Reference Manual

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LCD Controller

The LCD controller contains a character-generator ROM (CGROM) with 192 preset 5x8 character
patterns (see table 4 below), a character-generator RAM (CGRAM) that can hold 8 user-defined 5x8
characters, and a display data RAM (DDRAM) that can hold 80 character codes. Character codes
written into the DDRAM serve as indexes into the CGROM (or CGRAM). Writing a character code into
a particular DDRAM location will cause the associated character to appear at the corresponding
display location. Display positions can be shifted left or right by setting a bit in the instruction register
(IR). The write-only IR directs display operations (such as clear display, shift left or right, set DDRAM
address, etc). Available instructions (and the associated IR codes) are shown in the right-most column
of table 3 below. A busy flag shows whether the display has competed the last requested operation;
prior to initiating a new operation, the flag can be checked to see if the previous operation has been
completed.

The display has more DDRAM locations than can be displayed at any given time. DDRAM locations
00H to 27H map to the first display row, and locations 40H to 67H map to the second row. Normally,
DDRAM location 00H maps to the upper left display corner, and 40H to the lower left. Shifting the
display left or right can change this mapping. The display uses a temporary data register (DR) to hold
data during DDRAM /CGRAM reads or writes, and an internal address register to select the RAM
location. Address register contents, set via the IR, are automatically incremented after each read or
write operation. The LCD display uses ASCII character codes. Codes up through 7F are standard
ASCII (which includes all “normal” alphanumeric characters). Codes above 7F produce various
international characters – please see the manufacturer’s data sheet for more information on
international codes.

The PmodCLP is connected to the system boards by one dual and one single Pmod connector. The
interface includes eight data and three control signals that are routed from the Pmod connectors to
the LCD controller IC via simple resistor-diode voltage translation circuits. Power (3.3V or 5V) and
GND are routed to the LCD controller, and to a 3.3V-to-5V boost regulator that produces the 5VDC
required by the LCD panel itself. The voltage translation circuit ensures the eight data signals are
returned to the system board at 3.3V (as mentioned, if 5V signals are required, the regulator at IC1
can be removed). The three LCD control signals include RS (Register Strobe) that clocks data into
registers, the R/W signal that determines bus direction, and the E signal that enables the bus for read
or write operations. Pmod connector pin definitions are shown below, and following that is a figure
showing LCD bus signals and timings.

Table 1. PmodCLP Connector Signals

Pin No. Symbol Signal Description

J1.5, J1.11,
J2.5

J1.6, J1.12,
J2.6

J2.1 RS Register select: high for data transfer, low for instruction register
J2.2 R/W Read/write signal: high for read mode, low for write mode
J2.3 E Read/write strobe: high for read OE; falling edge writes data
J2.4 No Connect Optional back-light enable (not connected on PmodCLP)
J1.1,2, 3, 4

J1.7,8,9,10

Vss Signal ground

Vdd Power supply (5V)

Data Bus Bi-directional 8-bit data bus

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Copyright Digilent, Inc. All rights reserved. Other product and company names mentioned may be trademarks of their respective owners.