#Keyboard serial interface how to#
#Keyboard serial interface install#
#Keyboard serial interface code#

My SPI port in the PSoC Creator schematic window. I connected the slave-select input (ss) internally to a logic 0, so the SPI block stays active at all times.ДЇIGURE 4. The keyboard clock connects to the SPI serial-clock input (sclk). The MOSI (master-out, slave-in) pin connects to the keyboardвЂ™s data-output signal. Configure an SPI Port for 11 BitsДЇigure 4 shows an SPI slave port as I configured it. The documentation for each block lists the APIs and explains their uses. When you вЂњbuildвЂќ a project, the PSoC creates the APIs for you. Each block has its own datasheet, and example programs give you a head start. In most cases, you donвЂ™t need to set bits in registers. You select a function, drag its block into the PSoC Creator schematic drawing area, and set parameters. Unlike other MCUs, the 5LP devices only implement (or вЂњconnectвЂќ) the blocks you want. (Directions are included with the article downloads.)ДЄ Cypress 5LP PSoC (Programmable System-on-a-Chip) device includes many вЂњbuilding blocksвЂќ for functions such as SPI, USB, and UART ports EEPROM clocks analog-to-digital converters (ADC) pulse-width modulators (PWM) and so on. Print the documents, вЂњPSoC 5LP Prototyping Kit GuideвЂќ and Cypress AN77759 вЂњGetting Started with PSoC 5LP,вЂќ and use them to get off to a quick and easy start. Photo courtesy of Cypress Semiconductor Corp. These signals communicate data and programs between the PSoC chip and your host PC.

The four contacts on the left mate with a female USB connector. The board connects to a PC via a USB cable.ДЇIGURE 3.

#Keyboard serial interface install#

It does not discuss auxiliary keys such as Home, Page Up, and Page Down, but you may easily modify the software to include them if you wish.ДЇor this project, I chose a Cypress Semiconductor CY8CKIT-059 5LP prototyping kit ( Figure 3) and the free Cypress PSoCв„ў Creator software you can download and install on a host PC. This article covers the keys in the large main alphanumeric keyboard area. The MCU can then process the information and act accordingly. In this mode, the keyboard can supply the needed serial data and clock signals. Many MCUs include a serial-peripheral interface (SPI) port that can operate as a slave device and receive serial data. You might think a UART could handle this serial information, but keyboard clock frequencies can vary between 10 kHz and about 16 kHz, so a UART set for a fixed bit rate might not work in all cases ( Note 1).

#Keyboard serial interface code#

A PS-2 keyboard transmits data and clock signals when I press the W key, which has the assigned code 0x1D (MSB first). The least-significant bit (LSB) of a key code gets shifted out first.ДЇIGURE 1. A PS-2 keyboard does, however, transmit key codes in a UART-type format: a start bit eight data bits an odd-parity bit and a stop bit ( Figure 1). These codes donвЂ™t directly translate into ASCII values 0x57 and 0x58, respectively. So, for example, the W key produces 0x1D and the X key produces 0x22 (all values given in hexadecimal). The PS-2 keyboard engineers assigned a unique code to each key.

#Keyboard serial interface how to#

I'll show you how to use a system-on-a-chip and a bit of software to convert PS-2 key codes to corresponding ASCII values.

To further complicate things, these keyboards have their own code-transmission protocol. You can buy inexpensive PS-2 keyboards, but they don't produce ASCII values many applications need.