Week 8 of FYP 1

Date: 06/11/2013 (Wednesday)

Title: Research and Findings (PIC 16F877A)

ANALYSIS

Moving up the Microchip PIC16F Microcontroller family, we have the PIC16F877A. This is a very common MCU and it’s always mentioned in DIY projects. It’s popular among students, hobbyist and even engineers because it’s cheap. It is cheaper than its little brother which is the PIC16F84A. Another reason is the sheer amount of input and output pins available on this MCU. Among other things, this MCU also has Analog to Digital conversion capability without the need of an external chip.

PIC (Peripheral Interface Controller) is the IC which was developed to control peripheral devices, alleviating the load from the main CPU (Control Processing Unit). Compared to a human being, PIC is equivalent to the autonomic nervous system. The PIC, like the CPU, has calculation functions and memory, and is controlled by the software. However, the throughput and the memory capacity are low. Depending on the kind of PIC, the maximum clock operating frequency is about 20 MHz and the memory capacity to write the program is about 1000 to 4000 words. The clock frequency determines the speed at which a program is read and an instruction is executed. The throughput cannot be judged with the clock frequency alone. It changes with the processor architecture. However within the same architecture, the one with the highest clock frequency has the highest throughput.

The PIC is convenient for making calculations. The memory, the input or output ports and so on are incorporated into the IC (Integrated Circuit). The efficiency and the functions are limited, but the PIC can do the job of many IC's with software. Therefore, the circuit can be compact. Among all the PIC MCU families, the popular PIC16F877A was chosen because of its variety of hardware modules needed for most applications.

PIC 16F877A

Device Programmers

Devices called "programmers" are traditionally used to get program code into the target PIC. Most PICs that Microchip currently sells feature ICSP (In Circuit Serial Programming) and/or LVP (Low Voltage Programming) capabilities, allowing the PIC to be programmed while it is sitting in the target circuit. ICSP programming is performed using two pins, clock and data, while a high voltage (12V) is present on the Vpp/MCLR pin. Low voltage programming dispenses with the high voltage, but reserves exclusive use of an I/O pin and can therefore be disabled to recover the pin for other uses (once disabled it can only be re-enabled using high voltage programming).

There are many programmers for PIC microcontrollers, ranging from the extremely simple designs which rely on ICSP to allow direct download of code from a host computer, to intelligent programmers that can verify the device at several supply voltages. Many of these complex programmers use a pre-programmed PIC themselves to send the programming commands to the PIC that is to be programmed. The intelligent type of programmer is needed to program earlier PIC models (mostly EPROM type) which do not support in-circuit programming.

Many of the higher ends flash based PICs can also self-program (write to their own program memory). Demo boards are available with a small boot loader factory programmed that can be used to load user programs over an interface such as RS-232 or USB, thus obviating the need for a programmer device. Alternatively there is boot loader firmware available that the user can load onto the PIC using ICSP. The advantages of a boot loader over ICSP is the far superior programming speeds, immediate program execution following programming, and the ability to both debug and program using the same cable.

Programmers/debuggers are available directly from Microchip. Third party programmers range from plans to build your own, to self-assembly kits and fully tested ready-to-go units. Some are simple designs which require a PC to do the low-level programming signalling (these typically connect to the serial or parallel port and consist of a few simple components), while others have the programming logic built into them (these typically use a serial or USB connection, are usually faster, and are often built using PICs themselves for control).

PIC Programmer (Program Burner)

Crystal Oscillator (20MHz)

PIC 16F877A has an on-chip RC oscillator but it is used for ADC operation. But the external oscillators (usually 4 - 20MHz) are required for operating the PIC.