PicoLCD

There are several displays going by the PicoLCD name, I have the 20 character, 2 line version (20x2). It connects to the host as a USB HID device.

The folks at Mini-Box were kind enough to respond with both schematics and source code for my PicoLCD 20x2 display. They have everything up on their web page now, see http://www.mini-box.com/picoLCD-20x2-OEM

Now I can do something fun with it. Well. Let's say "More fun." I was already able to get it going on 8track with the generic lcd4linux program, but I want to be able to use all the extra ports on it. What I have in mind requires programming the actual board.

Features

LCD: 20 characters wide, 2 rows, with backlight
CPU: Microchip 18F4550 (Microchip page)
This chip has 32K of Flash, 2K RAM, a 13 channel 10-bit ADC, a couple comparators, and of course the 11Mbps USB port.
One bit switch
64k EEPROM
IR port

There are many interesting features on this board considering on the surface it's just a 20x2 LCD. A companion product from Mini-box is a board with buttons and an IR receiver on it. I don't have one of those, and it would not fit in 8track anyway.

One bit switch NC7SZ384: The board has connectors for "power in", "power out", and a "power button". The power in and and out are wired up to the switch. The "power button" is simply connected to a port on the CPU. From the docs I think Mini-box intended this to work with the host PC power connections.

USB connection to host

There are cables available but alas I neglected to order any.

The Mini-box docs show a 5 pin connection, but my board has only 4 pins, no ground wire so I ignore that connection. On my Epia motherboard I connected to the on board USB using a 6 pin cable that I had handy. The Epia gives me 4 options, I choose a set up that leave the other three available. It looks like this

LCD    CABLE  EPIA
        
1 V+   6 YE    10
2 D-   5 GN    12
3 D+   4 WH    14
4 V-   3 BK    16
5 GND  2 OR    nc
       1 RD    nc

Using the PicoLCD with lcd4linux

Not going to go into a lot of detail here, but this is available for most Linux distributions and it supports the PicoLCD 20x2.

You have to enable the 20x2 by commenting out the default setup line and uncommented the 20x2 line in the lcd4linux config file.

Then you can pick and choose what you want displayed from the included tools or write scripts for lcd4linux to run.

Working with the SDK

Mini-box provides an SDK so that you can write your own host-based code. The SDK includes a simple sample program.

You can use the sample program instead of lcd4linux if you don't want to do programming.

Programming the PicoLCD

You need a development system to run Microchip's PIC development tools. I use the MPLAB X version on Linux. I use the XC 8 compiler. All free now.

Minibox provides a separate bootloader and firmware. Minibox used the C18 compiler. I wonder how XC8 compares?

Bootloader

There is an app note from Microchip on bootloaders. http://ww1.microchip.com/downloads/cn/AppNotes/cn_00851b.pdf

The bootloader is stored in 256 bytes protected memory and it will load new firmware into program flash; that way you don't need an ICSP programmer to put new firmware into the PicoLCD.

Reading the bootloader source code: It will try to load new firmware via USB if

1. "Flasher is Summoned" I have no idea what this means
OR 2. You hold down the up/down keys at boot time
OR 3. there is no program in firmware

This bootloader looks like it came straight from Microchip, with a customized user/user.c file.

Port assignments

RA0	LED0	output
RA1	LED1	output	transistor driver
RA2	LED2	output
RA3	LED3	output
RA4	LED4	output
RB5	LED5	output
RB0	I2C SDA		I2C serial data
RB1	I2C SCL		I2C serial clock
RB2
RB3	LCD BIAS	output
RB4	PWR0	output	controls power switch
RB5	PWR1	input	push button "power"
RB6	ICD PGC	input	ICD pin 6
RB7	ICD PGD	input	ICD pin 4
RC4	USB D-	output	USB connector
RC5	USB D+	input	USB connector
RC6	SERIAL TX	output	USART connector
RC7	SERIAL RX	input	USART connector
RD0	ROW1	input	keypad scan and lcd scan
RD1	ROW2	input	keypad scan and lcd scan
RD2	ROW3	input	keypad scan and lcd scan
RD3	ROW4	input	keypad scan and lcd scan
RD4	COL1	output	keypad scan
RD5	COL2	output	keypad scan
RD6	COL3	output	keypad scan
RD7	COL4	output	keypad scan
RE0	LCD RS	output
RE1	LCD EN	output
RE2	LCD Backlight	output

Power switch

There is a NC7SZ384 power switch on the board that can switch up to 128 ma and 0-7v. It is on port RB4; you can turn on and off some accessory of your choice using this switch. There is a "power button" on RB5, it's just another pushbutton grouped with the power switch.