User Interface - Lcd Driver Based On The HT1621 Controller

Application Note Abstract This Application Note describes implementation of a liquid crystal Display (LCD) driver based on the widely available HOLTEK HT1621 LCD Controller Methods and algorithms of Display control are described and an API library is provided. The LCD used in this example was a customer’s custom part. The proposed algorithms CAN be easily adapted to any custom LCD panel connected to the controller. Introduction LCDs are widely used as data Display devices in embedded systems. Among the features that have made LCDs popular are low price, low power dissipation, lightweight, durability, reliability, and broad support by dedicated ICs for Communication with Microcontrollers A good example of an LCD Driver is the Hitachi character LCD Driver HD44780, the industry standard. This dot-matrix LCD Controller is supported by PSoC APIs. It is useful in applications that permit alphanumeric data Display However, specialized Displays are often needed. Specialized Displays keep end- product prices low, simplify the Interface between the Microcontroller and LCD Driver and decrease weight and size parameters. Examples of specialized Displays include Clocks calculators, telephones, and home and industrial appliances. This implementation is based on one of these dedicated drivers, the HT1621. This Application Note addresses the proposed implementation in two parts: ƒ General Description ƒ LCD Driver Implementation General Description The HT1621 driver is a 128-segment (32x4), multi-functional LCD Driver with memory mapping. The software configuration feature of HT1621 makes it suitable for many LCD applications, including LCD modules and Display subsystems. Only three or four connections are required for interfacing between the host controller and the HT1621. A structural schematic of the Display system is shown in Figure 1. This structure requires few external components and uses only three Interface connections. The system consists of the PSoC, HT1621 controller, and an LCD panel. The HT1621 besides its primary function as an LCD controller, has peripherals including the watchdog Timer time base generator and the Tone frequency generator. For more information about these features, refer to the HT1621 data sheet. Note that the controller has an on-chip RC Oscillator (256 kHz) for controlling the LCD and peripherals. This General Description focuses on the components and functions of the HT1621 driver that relate directly to the LCD: ƒ Display Memory RAM ƒ LCD Driver in HT1621 ƒ Command Format ƒ Interfacing with HT1621

Microcontroller interface using RS485 & RS422

After a period of research, I found out that RS485 and RS422 is in fact the same.

RS422 is a duplex configuration. RS422 using 4 wire to communicate in both direction. One pair of wire to do transmit and the other pair to receive. Both sides is able to transmit and receive at the same time.

RS485 is a half duplex configuration. RS485 using only 2 wire to communicate in both direction. With only two wire, it means that when one side is transmitting, the other side of the communication line will be receiving. Both side cannot be transmitting at the same time. For RS485 transceiver, use MAX485 or MAX3485. They have the same pin out except that MAX485 uses 5V supply, MAX3485 uses 3.3V supply.

RS422 can be connected to work with RS485 to either receive or transmit date, but not both. RS422 can be wired directly using a pair of wire, +ve to +ve, -ve to -ve terminal. For RS422 transceiver, use MAX488 or MAX3488. They have the same pin out except that MAX488 uses 5V supply, MAX3488 uses 3.3V supply.