HP LaserJet 4500 front panel

Here is front panel from HP LaserJet 4500 printer. It has 2×16 LCD (probably with Hitachi HD66710 controller, but I am not sure because there are no markings on the board) , 3 LED indicators and 9 push buttons.

On the back PCB there are 20 pin LCD connector (J702) and 7 pin connector (J701). LCD module also has 20 pin connector (CN1).

CN1 , J702 and J701 pinout:

           

Description	7 pin connector (J701)	20 pin connector (CN1 and J702)
GND	7	19
3.3V	1	18
5V (backlight)	2	20
SEL	5	14
CLK (SCLK)	6	15
DIN (MOSI)	4	17
DOUT (MISO)	3	16

http://playground.arduino.cc/Code/HpLaserJetLcd.

Here you find all information about connecting this panel to Arduino. ( Uses software SPI bit banging ).

I used source code from above site and ported it to STM32F103RBT6  microcontroller development board with hardware full duplex 16bit SPI.

Some notes about LCD :

• No lowercase letters.
• No blinking cursor.

Here is initialization of SPI ( CPU runs 72Mhz,  SPI speed is 562.5kHz ):

GPIO_InitTypeDef GPIO_InitStructure;
SPI_InitTypeDef SPI_InitStructure;
NVIC_InitTypeDef NVIC_InitStructure;

_selectPin = GPIO_Pin_4;
_selectPin_gpio = GPIOA;
_clockPin = GPIO_Pin_5;
_clockPin_gpio = GPIOA;
_dataWritePin = GPIO_Pin_7;
_dataWritePin_gpio = GPIOA;
_dataReadPin = GPIO_Pin_6;
_dataReadPin_gpio = GPIOA;

RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA | RCC_APB2Periph_SPI1, ENABLE);

GPIO_StructInit(&GPIO_InitStructure);
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
GPIO_InitStructure.GPIO_Pin = _clockPin | _dataWritePin;
GPIO_Init(GPIOA, &GPIO_InitStructure);

GPIO_StructInit(&GPIO_InitStructure);
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_Out_PP;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
GPIO_InitStructure.GPIO_Pin = _selectPin;
GPIO_Init(GPIOA, &GPIO_InitStructure);

GPIO_ResetBits(_selectPin_gpio,_selectPin);
GPIO_ResetBits(_clockPin_gpio,_clockPin);
GPIO_ResetBits(_dataWritePin_gpio,_dataWritePin);

GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN_FLOATING;
GPIO_InitStructure.GPIO_Pin = _dataReadPin;
GPIO_Init(GPIOA, &GPIO_InitStructure);

NVIC_InitStructure.NVIC_IRQChannel = SPI1_IRQn;
NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 4;
NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0;
NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
NVIC_Init(&NVIC_InitStructure);

SPI_InitStructure.SPI_Direction = SPI_Direction_2Lines_FullDuplex;
SPI_InitStructure.SPI_Mode = SPI_Mode_Master;
SPI_InitStructure.SPI_DataSize = SPI_DataSize_16b;
SPI_InitStructure.SPI_CPOL = SPI_CPOL_High;
SPI_InitStructure.SPI_CPHA = SPI_CPHA_2Edge;
SPI_InitStructure.SPI_NSS = SPI_NSS_Soft;
SPI_InitStructure.SPI_BaudRatePrescaler = SPI_BaudRatePrescaler_128;
SPI_InitStructure.SPI_FirstBit = SPI_FirstBit_MSB;
SPI_InitStructure.SPI_CRCPolynomial = 7;
SPI_Init(SPI1, &SPI_InitStructure);

SPI_Cmd(SPI1, ENABLE);
SPI_I2S_ITConfig(SPI1, SPI_I2S_IT_RXNE, ENABLE);

Sending data to panel:

void sendLcdByte(uint8_t value, uint8_t mode)
{
  uint16_t wordValue = (mode) ? 0 : 0x80; // State of the RS (0 - Data, 1 - Instructions)
  wordValue |= (uint16_t)_digitalSwitchMask;
  wordValue |= ((uint16_t)(~value)<<8); 
  while (SPI_I2S_GetFlagStatus(SPI1, SPI_I2S_FLAG_TXE) == RESET); 
  SPI_I2S_SendData(SPI1,wordValue); 
  GPIO_SetBits(_selectPin_gpio,_selectPin); 
  GPIO_ResetBits(_selectPin_gpio,_selectPin); 
  delay_us(50); // commands need > 37us to settle
}

Reading state of the 9 buttons from panel ( 9 bits represent state of 9 buttons ):

extern uint16_t inputValues;

void SPI1_IRQHandler(void) {

  if(SPI_I2S_GetITStatus(SPI1,SPI_I2S_IT_RXNE)==SET)
  {
     inputValues = SPI_I2S_ReceiveData(SPI1) >> 5;
  }
}

The source code for the project is available at my github:HP_4000_4500. The source code is the same for HP 4000 and HP 4500 panels. The only difference is the initialization of the SPI.

Here is video showing demo :

Left button press toggles led. Right button press turns led on and turns led off when released. Select button toggles all three leds. Small red button turns off backlight, and big green button turns the backlight on. On the screen there is a counter that is incremented every millisecond and a “heart” that flashes every second.