LCD_notes

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Special topic #1: LCD Module on DE2 Board

In this section, an application example of FSM for LCD display will be presented. In order to

use the LCD module on DE board, appropriate data communication between F!"# and LCD

module is re$uired. %ne can desi&n an FSM to achie'e this communication. First, F!"# lo&ic

&enerates di&ital cloc( si&nals )hours, minutes, and seconds*+ then an FSM desi&ned in F!"#

deli'ers the di&ital cloc( si&nals to LCD module, accordin& to interface re$uirements, such as

data format and timin& constraints.

1. LCD module on DE2 board

%n the #ltera DE F!"# de'elopment board, there is a Li$uid Crystal Display )LCD*

module that can be used to display text by sendin& appropriate commands from F!"# chip to the

LCD module. here is a built-in controller D//012 in the LCD module to dri'e the display. he

interface between F!"# chip and the LCD module is shown in Fi&.3.

Fi&.3 he interface between F!"# chip and LCD module

LCD4%5 )hi&h-acti'e* turns on the power of LCD module.

LCD46L%5 controls the LCD bac( li&ht.

LCD4D## 72809 is an 1-bit data bus for their data communication.

LCD4:; defines the direction of data bus )LCD4:;3?+ LCD4D## is a command )display clear, cursor shift and address information

etc.* if LCD4:S is >2?.

FPGA

LCDd

isplay

(controllerHD44780

included)

LCD_ON

LCD_BLON

LCD_RW

LCD_RS

LCD_EN

LCD_DATA[0:7]

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he F!"# pin assi&nment of the interface is shown in able.3.3.

able 3.3 LCD related pin assi&nments on DE

2. Function description of LCD module

1) Registers, DDRAM, and CR!M in LCD module

he controller D//012, built in LCD module, plays an important role in the LCD display

tas(. he controller communicates with F!"#, and controls the LCD display. he bloc( dia&ram

of D//012 is shown in Fi&..

he D//012 has two 1-bit re&isters )I:, and D:* to store information sent from F!"#.

he operation and selection of two re&isters are defined by able 3.. he I: )instruction

re&ister* stores instruction codes, such as display clear, cursor shift, and address information for

display data :#M )DD:#M* and character &enerator :#M )C":#M*. he I: can only be

written from F!"#. he D: )data re&ister* temporarily stores data to be written into DD:#M or

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C":#M and temporarily stores data read from DD:#M or C":#M. ere we only consider the

situation that data are written into DD:#M or C":#M. So, in our followin& discussion,

LCD4:; is always set to >2? for writin& only, unless otherwise stated. 6y LCD4:S, the data

LCD4D## 72809 is interpreted either as instruction codes )when LCD4:S

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able 1. :e&ister Selection

Fi&.@ the relationship between DD:#M addresses and positions on LCD

he address counter )#C* recei'es an initial address throu&h I: based on a

command=instruction code, and assi&ns and updates addresses to both DD:#M and C":#M.

he DD:#M is used to store the display data represented in 1-bit character codes and sent from

F!"#. Each address of DD:#M corresponds to a position on the LCD. he relationship between

DD:#M addresses and positions on LCD is shown in Fi&. @ )-by-3A character display*.

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C"aracter enerator R!M #CR!M)$ he C":%M &enerate Bx1 dot or Bx32 dot

character patterns from 1-bit character codes. See able 3.@. For example, in order to display on

the first line position B, 1h@ should be written into the address )#C* 1h2/ of DD:#M.

able 3.@ C":%M pattern )Bx1 dots*

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2) %nstruction table

able 3./ includes all a'ailable instructions to control LCD. he M!=F!"# will send a

se$uence of instructions to LCD with appropriate timin& constraints. he instructions are di'ided

into two types8 3* command+ * data transfer. he command instructions ):S

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&) 'iming re(uirements

he M!=F!"# should meet the followin& timin& re$uirements when it communicates with

LCD. For write operation#:=;

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& %nitialiing of LCD

F!"# chip needs to send a series of initialiation commands to initialie the LCD. hese

commands include function set, display off, display clear, and entry mode set. he datasheet

pro'ides a typical initialiation process shown in Fi&.B.

Fi&. B Initialiation steps

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*. F+Acore LCDDispla-$ LCD panel c"aracter displa-

C!M+!E' LCD4Display

+!R')ex4Display4Data8 % /'DL!%C0EC'!R

))5um4ex4Di&its/*-3 D!'! 2*+

reset, cloc(4/1M8 % /'DL!%C+LCD4:S, LCD4E8 !' /'DL!%C+

LCD4:;8 %!' /'DL!%C+

D##46S8 %!' /'DL!%C0EC'!R)0 D!'! 2**+ED C!M+!E'3

he LCD4Display core is used to display static #SCII characters and chan&in& hex 'alues

from hardware on the DEs 3A by line LCD display panel. he cores GDL code can be

confi&ured internally by the user to display different #SCII strin&s and hex data fields.

Instructions can be found in comments in the cores GDL code. # "eneric,Num_Hex_Digits, is

used to set the sie of the ex4Display4Data input )i.e., Each hex di&it displayed re$uires a /-bit

si&nal*. he LCD controller datasheet contains information on &raphics characters and LCD

commands. # state machine is used to send data and commands to the LCD controller and to

&enerate the re$uired handsha(e si&nals.

ex4Display4Data contains the /-bit hexadecimal hardware si&nal 'alues to con'ert to

#SCII hex di&its and send to the LED display. he "eneric, 5um4ex4Di&its, adHusts the sie of

the input hex data.

LI6:#: IEEE+SE IEEE.SD4L%"IC433A/.all+

SE IEEE.SD4L%"IC4#:I.all+

SE IEEE.SD4L%"IC45SI"5ED.all+

-- S;1 )"L%6#L :ESE* resets LCD

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E5I LCD4Display IS

-- Enter number of li'e ex hardware data 'alues to display

-- )do not count #SCII character constants*

"E5E:IC)5um4ex4Di&its8 Inte&er8< *+

--

!%:)reset, cl(4/1Mh 8 I5 SD4L%"IC+ex4Display4Data 8 I5 SD4L%"IC4GEC%:))5um4ex4Di&its/*-3 D%;5% 2*+

LCD4:S, LCD4E 8 % SD4L%"IC+

LCD4:; 8 % SD4L%"IC+

D##46S 8 I5% SD4L%"IC4GEC%:)0 D%;5% 2**+

E5D E5I LCD4Display+

#:CIEC:E a %F LCD4Display IS

!E character4strin& IS #::# ) 2 % @3 * %F SD4L%"IC4GEC%:) 0 D%;5% 2 *+

!E S#E4!E IS )%LD, F5C4SE, DIS!L#4%5, M%DE4SE, !rint4Strin&,

LI5E, :E:54%ME, D:%!4LCD4E, :ESE3, :ESE,

:ESE@, DIS!L#4%FF, DIS!L#4CLE#:*+

SI"5#L state, next4command8 S#E4!E+SI"5#L LCD4display4strin& 8 character4strin&+

-- Enter new #SCII hex data abo'e for LCD DisplaySI"5#L D##46S4G#LE, 5ext4Char8 SD4L%"IC4GEC%:)0 D%;5% 2*+

SI"5#L CLJ4C%54/22K8 SD4L%"IC4GEC%:)3 D%;5% 2*+

SI"5#L C#:4C%58 SD4L%"IC4GEC%:)/ D%;5% 2*+

SI"5#L CLJ4/22K4Enable,LCD4:;4I5 8 SD4L%"IC+

SI"5#L Line34chars, Line4chars8 SD4L%"IC4GEC%:)30 D%;5% 2*+

6E"I5

LCD4display4strin& < )-- #SCII hex 'alues for LCD Display

-- Enter Li'e ex Data Galues from hardware here

-- LCD DIS!L#S E F%LL%;I5"8------------------------------

--N Count

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CLJ4/22K4Enable < R2R+

ELSE

IF CLJ4C%54/22K OP2E#A2P E5

CLJ4C%54/22K < CLJ4C%54/22K 3+

CLJ4/22K4Enable < R2R+ELSE

CLJ4C%54/22K < OP22222P+CLJ4/22K4Enable < R3R+

E5D IF+

E5D IF+

E5D !:%CESS+

!:%CESS )CLJ4/1MK, reset*

6E"I5IF reset < R2R E5

state < :ESE3+

D##46S4G#LE < OP@1P+

next4command < :ESE+

LCD4E < R3R+

LCD4:S < R2R+

LCD4:;4I5 < R3R+

ELSIF CLJ4/1MKREGE5 #5D CLJ4/1MK < R3R E5

-- State Machine to send commands and data to LCD DIS!L# IF CLJ4/22K4Enable < R3R E5

C#SE state IS

-- Set Function to 1-bit transfer and line display with Bx1 Font sie

-- see itachi D//012 family data sheet for LCD command and timin& details

;E5 :ESE3

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next4command < DIS!L#4%FF+

-- urn off Display and urn off cursor

;E5 DIS!L#4%FF

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ELSE

C#:4C%5 < P22222P+

E5D IF+

-- Uump to second lineV

IF C#:4C%5 < 3B E5 next4command < line+-- :eturn to first lineV

ELSIF )C#:4C%5 < @3* %: )5ext4Char < OPFEP*E5

next4command < return4home+

ELSE next4command < !rint4Strin&+ E5D IF+

-- Set write address to line character 3

;E5 LI5E

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