BootLoader

What is BootLoader?

A Bootloader is the first program which executes (before the main program) whenever a system is initialized. In PC It is used to boot he OS of the system. In case of microcontrollers, a bootloader enriches the capabilities of the microcontroller and makes them self programmable device. This article will explore the significance of having bootloader in microcontroller.

 

While working with microcontroller a common problem faced is to program the controller? Different controllers follow different protocols to program their ROM and hence every controller has a different programmer, which is difficult to be made. A universal programmer on the other hand is quite costly.

 

With the upgrading era of technology, today’s microcontrollers are not only growing powerful but also incorporate technically superior functionality which makes them more flexible and quite easy to use. The bootloader is one of them. A bootloader is a small section in the ROM of the controller which executes first when it is initialized. Generally the bootloader are written to empower a controller with self burning capabilities. The bootloader program can access any of inbuilt peripherals like USB, USART, CAN, SPI, etc. to exchange the data and this capability is used to write the flash memory. In automotive industries the controllers are encapsulated in a metal case and leaves accessibility to few pins only.. In such cases the controller is programmed with the bootloader program using CAN interface at the time of manufacturing and then it is pasted in the circuits, which provides an ease to update the code with time.

 

The bootloader can be inserted into a controller by using an external or any conventional burner and then depending on the type of bootloader the controller starts responding to the interface. So whenever the controller is reinitialized the program counter jumps to the bootloader section and then it waits there for the instruction, which is fed from external device. In case there is no bootloader the program counter will go on 0000H (starting position of the flash memory) and start executing the instructions which are written in the memory of the device.  

 

If the program counter enters the bootloader section then after executing the bootloader, there must be an instruction in the bootloader which will force the program counter to go to 0000H.

 

Mostly the bootloader resides in the bottom most area of the ROM but there are some cases where the boot loader can be configured in the top (like in PIC18F).The starting and ending address of the bootloader in the ROM depends on the product. So it’s recommended to use the datasheet to collect the required information

COB ICs

The quest to fabricate more and more devices in a minimum Silicon space has been ON since J. K and R. Noyce invented the first ICs. This quest has enabled scientific community to cross various technological frontiers. Sustained efforts to put more and more transistors on a wafer have led us to nanotechnologies.

 

In the commonly used electronic technology, the semiconductor chips (also known as bare-dice) are individually mounted on a package, and wire-bonded to its I/O pins. This package is then mounted on a Printed Circuit Board (PCB). However, not only does packaging of single chip ICs cost more than the cost of the chips they contain, packaging of a chip take relatively large amount of physical space. Using a conventional single chip package and circuit board interconnect strategy, the package and interconnects took up over 50% of the timing budget as well.

 

However, there is an emerging technology where several bare die chips are mounted on a single package. This technology is known as Multi-Chip Module (MCM) technology. It can be used for both standard and ASIC chips. The resulting package can then be soldered on a PCB.

 

Although different from MCM, Chip-on-Board (COB) and Flip-Chip technologies are generally considered as related technologies. In COB technology, a semiconductor chip is placed directly on a PCB, eliminating the packaging step thereby, COB comprises of bare dice on organic laminate substrates, such as FR4, along with other SMT devices, both packaged devices and discrete components.  

 

In the Flip-Chip technology, the chip is mounted upside-down (metal contacts down), providing a direct electrical connection to the I/O pads, eliminating the wirebonding step.

CMOS Image Sensors

Advent of CMOS technology in eighties led to the phenomenal growth in semiconductor industry. Transistors have become smaller, faster, consume less power, and are cheaper to manufacture. It is CMOS technology which has enabled very high integration on the chips leading to modern high performance, miniaturized integrated circuits.

 

Apart from the valuable contribution in miniaturization of integrated circuits, CMOS technology found applications in sensing applications. CMOS technology has been adopted to design sensors, especially in the field of imaging. Due to the wide usage of CMOS based image sensors, CMOS sensors are often considered to be a synonym of CMOS based image sensors and have emerged as a competitor to CCD based image sensors.

 

Until recently, Charge Coupled Devices (CCDs) dominated most of the image sensing systems, i.e., cameras, camcorders, etc. CCDs have been in use in astronomical cameras, video camcorders and scanners. However of late, CMOS Imaging have emerged as an alternative to CCD imagers and it also offers better features.

 

Subsequent sections will discuss both CCD and CMOS sensor based imagers, their pros and cons, and also their applications. Further, other applications of CMOS technology in the field of sensing will be discussed.