esp32_hdsp2112

A sample ESP32 application for two vintage HDSP-2112 displays, driven with two MCP23s17 16-bit I/O expander. Tested with VSCode + platformio and a 38pin ESP32 NodeMCU board.

[env:esp32dev]
platform  = espressif32
board     = esp32dev
framework = arduino

1. Schematic

1.1. Wiring of multiple MCP23s17

The data sheet states that it is possible to connect multiple MCP23s17s to a SPI bus in parallel with one single CS signal only. Follow these steps:

1.1.1. Pre-assign address pins A0..A2

Each MCP23s17 module requires a unique address, that is done with the wiring of the address pins A[0..2]. The pre-assigned address pins in this setup are:

device	A0	A1	A2	SPI-control	Comment
U1	0	0	1	01000001x	GPA=d[0..7], GPB=a[0..4]
U2	1	1	1	01000111x	GPB=[res,fl,wr,rd,cs0,cs1]

1.1.2. Activate HAEN bit (hardware-address-enable) in IOCON register

When initializing the two MCP23s17, the HAEN bit (=hardware address enable) must be set within the IOCON register (=I/O expander configuration). That is done by calling the member function enableAddrPins()

  m_U1.enableAddrPins();  // enable HAEN function
  m_U2.enableAddrPins();  // enable HAEN function

1.1.3. Select the MCP23s17 devices via SPI-control-byte

The devices are selected via the SPI control byte according to the pre-assigned address pins A0..A2

see mcp23s17.pdf , Figure 3-5: SPI-Control-Byte Format, page 15

This is automatically handled within the driver. The specific addresses are set during initialization of the SPI-bus within the begin_SPI() member function.

  m_U1.begin_SPI(m_spi_cs,m_spi_clk,m_spi_miso,m_spi_mosi,U1_addr);
  m_U2.begin_SPI(m_spi_cs,m_spi_clk,m_spi_miso,m_spi_mosi,U2_addr);

1.2. Wiring ESP32 SPI bus

The table below shows the wiring of the SPI connections for the ESP32 and the MCP23s17, i.e. the standard SPI bus of the ESP32 (VSPI)

ESP32-GPIO	MCP23s17 U1	MCP23s17 U2	Comment
05	11	11	SPI_CS, VSPI chip-select
18	12	12	SPI_CLK, VSPI clock
23	13	13	SPI_MOSI, VSPI master-out-slave-in
19	14	14	SPI_MISO, VSPI master-in-slave-out

1.3. Wiring the HDSP-2112 displays

The HDSP-2112 displays are connected in parallel, and each is selected via its own chip-select signal (CS_0, CS_1)

To get a proper flashing function, the displays were wired (clock select SEL pin 11) so that the left display generates the clock FLASH_CLK for the right display.

SEL (Pin 11)	level	comment
U3	3.3V	CLK (pin 12) work as output of flash-clock
U4	GND	CLK (pin 12) work as input

See specification hp_HDSP-2112.pdf page 9: clock-select (CLS pin 11) and clock-input/output (CLK pin 12)

Note

The recommended supply voltage is [4.5V to 5.5V]. The circuit used here, operates the displays with 3.3V, which remains within the abs. maximum range [-0.3V to 7.0V] of the data sheet. Even with 3.3V the displays work reliably and are shining bright. Using 3.3V has the advantage that the MCP23s17 can be connected directly to the ESP32, i.e. no level shifters are required.

2. Considerations about SW

2.1. MCP23s17 Library

The Adafruit-MCP23017-Arduino-Library is used to control the MCP23s17 port expander

2.2. Parent Class

The class HDSP2112 is derived from the class Print , so the member functions like printf() can be used easily.

2.3. Useful member functions

Some member functions as follows

• Reset() resets the displays (via hardware signal)
• Clear() fills display with blanks
• SetFlashBits() and FlashMode() used to flash individual characters of the displays
• BlinkMode() lets the whole display blink
• SetBrightness() used to adjust the brightness
• Selftest() performs a selftest
• WriteChar() prints a given character
• printf() works link standard printf for printing strings
• SetUdcFont() set 16 user defined chars

2.4. utf8 handling

Some utf8 characters can be mapped to the internal character map, that is handled by the member function UTF8_to_HDSP(), e.g. Ä is mapped to 0x15 or alpha is mapped to 0x05

2.5. Selftest() function

The HDSP2112 self test is activated by setting cwrTEST=1 within the control-word-register. The datasheet states that the procecdure needs about 4 sec, I set the wait time to 7sec. Afterwards the cwrTSTOK bit of the control-word-register indicates the status of the test. cwrTSTOK=1 means that the test was OK else it Failed. Reading from the HDSP2121 means: change the MCP23s17's m_U1.pinMode() of the from OUTPUT to INPUT and set RD signal for the displays accordingly.

Note

During the tests I found out that a Reset() must be called after the Selftest() function, in order to avoid a strange behaviour of the BlinkMode and FlashMode functions.

2.6. Basic example

The following main.cpp shows a basic example:

#include "hdsp2112.h"
HDSP2112 d;    // create default instance

void setup() {
  d.Begin();   // int SPI, MCP23s17 and HDSP2112 displays
  d.printf("Hdsp2112-Display"); // print something to display
  delay(2000);
}

void loop() {
}