AN1302

DS01302A-page 4

 2009 Microchip Technology Inc.

FIRMWARE FUNCTION

DESCRIPTIONS

Among the functions of the bootloader firmware, some

of them are more important:

do_i2c_tasks

related events. The event decoding is based on the

SSPIF flag and the SSPSTAT register.

flash_memory read

: This function takes a 16-bit

value as a address parameter and returns the data

read from Flash memory at the specified location.

flash_memory_write

: This function has two param-

eters. The first one is a 16-bit value as an Address

Pointer. Please note that the address must be properly

aligned to an 8 word boundary. The second parameter

is a pointer to buffer containing the data being written.

It does not return any value (void).

flash_memory_erase

: Performs an erase operation

starting with the address specified as a parameter. 32

instruction words are erased in a row and the specified

address must be aligned to a 32 word boundary.

service_isr

: This function performs the interrupt for-

warding feature. It is implemented as a GOTO instruc-

tion. For more information see the following section.

INTERRUPT FORWARDING

The PIC16F1XXX enhanced core has the interrupt vec-

tor at 0x0004. This address is located in the area where

the bootloader firmware is located. To maintain the

interrupt functionality it is required that the Interrupt

Service Routine (ISR) be relocated at a different

address, in the application segment. In the bootloader

code, at the interrupt vector location ( 0x0004), a GOTO

instruction is present. The Interrupt Service Routine is

contained in the application code. The application code

is shifted by 0x200, leaving room for the bootloader in

the lower part of the Flash memory. It will also contain

the Interrupt Service Routine at 0x0204. The boot-

loader code will contain a "GOTO 0x0204" instruction.

When an interrupt occurs, the program counter ( PC)

jumps to 0x0004 in the bootloader segment. At this

address, the "GOTO 0x0204" instruction will cause the

PC to jump to 0x0204 in the application segment,

where the Interrupt Service Routine is located (see

Figure 1).

Please

notice

that

the

PIC16F1XXX

enhanced core features Automatic Context Saving.

The interrupt latency will be increased by the GOTO

instruction execution time. See the example demo

application(s) for more details.

MULTIPROCESSOR SYSTEM

protocol, the target microcontroller can be interfaced

with a larger microcontroller having more processing

power (such as a main processor in a multiprocessor

system). Several such devices can be connected in

own address (see Figure 2).

FIGURE 2:

MULTIPLE SLAVE DEVICES

CONNECTED TO THE SAME

BUS