In-circuit Serial Programming - Microchip PIC ICSP Family of Chips

Microchip PIC ICSP Family of Chips

fig 1 - Microchip ICSP programmer

Micro-controllers are typically soldered directly to a printed circuit board and usually do not have the circuitry or space for a large external programming cable to another computer. A separate piece of hardware, called a programmer is required to connect to an I/O port of a PC on one side and to the PIC on the other side. The type of programmer, how it connects to the PC, and the various advantages and disadvantages of each are not within the scope of this document. However, a short list of the features for each major programming type is given here.

1. Parallel port - large bulky cable, most computers have only one port and it may be inconvenient to swap the programming cable with an attached printer. Most laptops newer than 2010 do not support this port. Parallel port programming is very fast.
2. Serial port (COM port) - At one time the most popular method. Serial ports usually lack adequate circuit programming supply voltage. Most computers and laptops newer than 2010 lack support for this port.
3. Socket (in or out of circuit) - the CPU must be either removed from circuit board, or a clamp must be attached to the chip making access an issue.
4. USB cable - Small and light weight, has support for voltage source and most computers have extra ports available. The distance between the circuit to be programmed and the computer is limited by the length of USB cable - it must usually be less than 6 ft. This can make programming devices deep in machinery or cabinets a problem.

ICSP programmers have many advantages, with size, computer port availability, and power source being major features. Due to variations in the interconnect scheme and the target circuit surrounding a micro-controller, there is no programmer that works with all possible target circuits or interconnects. Microchip provides a detailed ICSP programming guide at ww1.microchip.com/downloads/en/devicedoc/30277d.pdf Many sites provide programming and circuit examples. They are easily found using a Google search.

PICs are programmed using five signals (a sixth pin 'aux' is provided but not used). The data is transferred using a two wire synchronous serial scheme, three more wires provide programming and chip power. The clock signal is always controlled by the programmer.

fig 2 - Typical programming communication