BPP-420L Programmer's Reference

This page describes the font and instruction set. For hookup, configuration and specifications, please see the hardware reference.

Table of Contents

Programming

Serial Communication

Character Set

Screen Layout

Control Codes

Escape Instructions

Other Pages

Index, Revision History

Hardware Reference

Product Description

Serial Communication

BPP-420s accept asynchronous serial at 2400 or 9600bps, 8 data bits, no parity, 1 or more stop bit(s), often called "N81." They will accept RS-232 input or inverted TTL. See the hardware reference for further information.

Character Set

BPP-420s display the standard LCD character set for character codes 32 to 127 (0x20-0x7F hex). Character codes 128-135 (0x80-0x87 hex) are custom characters that are used by the display's "Big-character" mode, and may be redefined for other purposes.

Character Set (Character code= row+column)

Screen Layouts

BPP-420 displays four lines of 20 characters each. Printing works as you would expect, flowing left to right and top to bottom (though you can use control-P to print at any position on the screen).

For example, starting with the display cleared (its power-up state), suppose you send the following 80 bytes of text:

The BPP-420L serial LCD module displays alphanumeric text on a 4x20 backlit LCD.

..here is how the text is displayed:

Screen Layout. Position = row+column.

The display's "Big-character" mode can generate full-screen-height numbers and letters--up to four letters/digits per screen. Big-mode symbols—consisting of dot/decimal point (.), hyphen/minus sign (-), colon (:) and space—take up one-half the width of other "big" characters.

Big Characters

Symbols and Spaces are 1/2 Width

Control Codes

BPP-420s understand a small set of control codes similar to our other text-mode displays (GLO, VFD, ILM, TRM). Codes not listed below (e.g., Null, 0) are ignored by the display.

NOTE: Switch 1 on the serial interface must be OFF for these control codes to work; see the hardware reference for more information.

Items marked with » can be clicked for tips or more detail.

Home (ctrl-A) 01 dec 0x01 hex

Moves the printing position to 0, the first character of the top line. »

For example, you clear the screen and send the text Hello— Hello appears at the upper left of the screen, in positions 0-4. Now you send ctrl-A, followed by J— Hello becomes Jello.

Begin Big-Character Mode (ctrl-B) 02 dec 0x02 hex

Puts the display into Big-character mode, in which characters are displayed as 4-line tall graphics. The display can show up to four big characters at a time. The big character set includes 0-9, A-Z (uppercase) and symbols dot/decimal point (.), hyphen/minus sign (-), colon (:) and space. The symbols take up one-half the width of the letter/number characters. To end big-character mode, send ctrl-C, another control code, or a character not available in big mode. »

When you send ctrl-B, text already on the screen is unaffected; the instruction changes the size of subsequent text. Numbers and letters are four columns wide followed by a blank column; symbols are two columns plus a blank. The display needs about 10ms to draw each big character, so updating the screen too rapidly in this mode will eventually overrun the serial buffer.

End Big-Character Mode (ctrl-C) 03 dec 0x03 hex

Sets the printing mode to the default size. »

When you send ctrl-B, text already on the screen is unaffected; the instruction changes the size of subsequent text.

Hide Cursor (ctrl-D) 04 dec 0x04 hex

Turns off the visible cursor. »

If the cursor is already off, has no effect.

Show Underline Cursor (ctrl-E) 05 dec 0x05 hex

Turns on an underline cursor that tracks the location of the next character to be printed. »

If the cursor is already on, has no effect.

Show Blinking-Block Cursor (ctrl-F) 06 dec 0x06 hex

Turns on a blinking-block cursor that tracks the location of the next character to be printed. »

If the cursor is already on, has no effect.

Bell (ctrl-G) 07 dec 0x07 hex

Pulses the Bell output (marked "J4") briefly to beep a 25mA piezo buzzer (if connected). »

The "+" side of J4 is connected to +5Vdc; the unmarked (-) pad is normally floating (open). For the Bell pulse, the controller grounds the (-) pad for approximately 100ms, then returns it to the open state.

Backspace (ctrl-H) 08 dec 0x08 hex

Backs up one character, erases that character, sets the print position to erased character's location. »

Behaves exactly like the Backspace key.

Tab (ctrl-I) 09 dec 0x09 hex

Moves the printing position to the next multiple-of-4 screen location: 0→4→8→12→16→20→24→... »

While it's normally better to use the ctrl-P position instruction, using tab to move around the screen may sometimes be convenient.

Smart Linefeed (ctrl-J) 10 dec 0x0A hex

Moves the printing position down a line. »

Each linefeed moves the printing position down one line. A linefeed received when the position is on the last line wraps back to the first line. If the display receives a carriage return/linefeed combination, it ignores the linefeed; that's what makes it "smart."

Vertical Tab (ctrl-K) 11 dec 0x0B hex

Moves the printing position up a line. »

Works like linefeed, but moves up instead of down. A Vtab received when the position is on the first line wraps back to the last line.

Clear Screen (ctrl-L) 12 dec 0x0C hex

Clears the screen and moves the printing position to 0—the first position of the first line. »

Use clear-screen sparingly. If you need to update a few characters on the screen, move to that position (using ctrl-P below) and print over the old characters. To update the entire screen, send Home (ctrl-A) and replace the screen contents with 80 brand-new characters. Clearing the screen unnecessarily causes an annoying blink effect.

Carriage Return (ctrl-M) 13 dec 0x0D hex

Moves to the first printing position of the next line. »

Same effect as a Home (ctrl-A) plus a linefeed (ctrl-J). Linefeeds paired with carriage returns are ignored.

Backlight On (ctrl-N) 14 dec 0x0E hex

Turns on the LED backlight. »

The backlight can be wired on by soldering a jumper across pads marked "BL_ON" on the serial interface.

Backlight Off (ctrl-O) 15 dec 0x0F hex

Turns off the LED backlight. »

If a jumper is soldered across "BL_ON" on the serial interface, ctrl-O has no effect.

Set Printing Position (ctrl-P) 16 dec 0x10 hex

Sets the printing position according to the value of the next byte, position+64 (0x40 hex). For example, to move to the fourth character of the third line (position 43; see the chart above), you would send two bytes, 16 107 (0x10 0x6B hex)»

It's not recommended for programming purposes, but you can also use a text number like "24" to specify ctrl-P position values. Text numbers must be followed by a throwaway character—like a space or a period—which will terminate the number but won't be displayed.

Right-align Text (ctrl-R) 18 dec 0x12 hex

Displays text (usually numeric) within a field 2 to 8 characters wide. The byte that follows ctrl-R is a text number from '2' to '8' (50-56 dec, 0x32-0x38 hex) that sets the field width. The text after that will be invisibly stored until one of the following is received:

• A control code.
• A period/decimal point.
• The specified number of bytes.

When this happens, the field will be cleared and the received text printed at the righthand end of the field. »

Right align works backward from the printing position in effect at the time. Make sure that there's enough space behind the printing position to avoid breaking the right-aligned text across lines. Does not work with big-mode text.

Escape: Start Multipart Instruction (ctrl-[) 27 dec 0x1B hex

See the Escape-code descriptions below.

Escape Instructions

These are multipart instructions that begin with the Escape character; 27 dec, 0x1B hex. Escape instructions affect memory: writing bitmaps to RAM to define custom characters, or storing/recalling text or character patterns to/from EEPROM.

Define Custom Character Pattern ESC D n B0 B1 B2 B3 B4 B5 B6 B7

Change the pattern of custom character n to the bitmap made up of bytes B0 through B7. The value n is a text number '0' to '7' (48-55 dec, 0x30-0x37 hex) specifying the custom character to be defined. Custom characters are located at 128-135 (0x80-0x87) in the character set; i.e., custom character 0 is 128, 1 is 129...

The default set of custom characters is used for big-character mode. Do not redefine custom characters if you're using big characters.

The figure below shows how the bits of bytes B0 through B7 define the shape of the custom character. The upper three bits of the pattern bytes are ignored. A tool for calculating custom-character bytes is online at seetron.com.

Bitmap Layout for Custom Characters.

An example: To define custom-character 3 (which maps to character code 131) to the °F pattern in the example above, you'd send the sequence of 11 bytes shown below.

Restore Default Custom Characters ESC E 1

Writes default bitmaps to all eight custom characters: ESC E (uppercase E; 69 dec, 0x45 hex) 1 (49 dec, 0x31 hex). If you have redefined custom characters, you must send this instruction before using big-character mode.