Readers should also study the page data sheet that covers the devices,. Microchip code DSA (see later). The following EPE subject material is. Note: The datasheet of PIC16FA Microcontroller and more detailed Features can be found at the bottom of this page. (Consult Sections of the 16F87x Data Sheet and of the Midrange Reference Manual for more detail.) Inside the 16F87x’s PWM module, the period is.

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When the RS input is negative the zener now acting as diode and the same resistors put a voltage on the interface pin that is close to zero. Program memory contains the programs that are written by the user. When no PC or download dongle is connected a resistor forces the interface pin to the opposite polarity of what it would be with the PC etc. The counter is automatically incremented to the next instruction during the current instruction execution.

The RS interface R2, D1, R7, R3 avoids current through the 16f protection diodes, which is outside Microchip’s operating specs and is rumored to cause all kinds of nasty effects. The user must disconnect the RS cable when the application program must run automatically after a reset.

Program memory write operations automatically perform an erase-before write on blocks of four words. By default a 16f is delivered with LVP enabled. When the pin assignment shown in the table is used the interface can be used both for HVP programming Wisp programmer and self-programming WLoader.

Hence the application loaded by the loader can be exactly the same as a stand-alone program downloaded to the 16f The final W is echoed as W when the programming is succesfull.

It is not needed for downloading using WLoader. It does not actually perform the write, but does verify against the datashert value, or in case of the configuration fuses word, against a copy of the actual fuses value.


Self-programming uses a program executed by the 16f itself. Luckily most compilers are not that clever. A production system could just provide the relevant signals on a 2×4 pin header, and rely on a download dongle that contains the remote reset and the RS circuitry. The remote reset circuit can be omitted when the target circuit already has a manual reset pushbutton switchbut it is very convenient to be able to reset the target and hence activate WLoader from the PC.

I recommend this version only to those who are enthousiastic about minimal-hardware solutions and can solve the problems that might occur. Leave a Reply Cancel reply Your email address will not be published. The 16f supports three methods to get a program into the chip: T Type The type name WLdr is copied to the communication buffer. The whole gadget can be plugged in where a 16f would fit and adds in-circuit downloading to a circuit.

The program counter PC executes these stored commands one by one. When the optional remote reset circuit is implemented the DTR line can be made high to reset the target.

Previous post Next post. The user application instructions at these addresses are put at a location within the loader, and are executed before the jump 16ff87x the rest of the user application program, starting at address 3.

Each time we write a new program to the controller, we ratasheet delete the old one at that time. When the target circuit must be kept as simple as possible the real or el-cheapo RS interface, and the remote reset circuit can be put in a download dongle.

This ‘el-cheapo’ version of the WLoader hardware uses a few resistors and a zener diode as RS interface. Hence the break condition and the hello commands are not needed, but do no harm.

Microchip keeps changing its website, so when these links turn out to be invalid you might have to look around a little.


WLoader – a 16f application loader

The final W is echoed as W when programming is not necessarry or the programming is succesfull. It is shown here mainly because this was the original WLoader hardware.

According to the type of the microcontroller, datasheef banks may vary. The banked arrangement is necessary because there are only 7 bits are available in the instruction word for the addressing of a register, which gives only addresses. I tested 20 and 10 MHz xtals at the WBus default baudrate of 19k2.

For data and configuration the higher 8 bits are set to 0. Once LVP is disabled in the configuration fuses word this pull-down might no longer be needed, but some people have reported that it is still needed for succesfull HVP programming. Note the resistor on the single line from the PIC used for communication.

WLoader – a 16f877 application loader

The send-receive combiner is just Darasheet. R Read The current memory location 4 hexadecimal digits is read and coped the content to the communication buffer. The 33k reset pull-up and a LED for power indication can be disabled by pulling two pin header jumpers for low-current tests. Loading the WLoader firmware disables it, so B3 is freed for use by the application.

Each time the main 16d87x execution starts at address — Reset Vector. The block diagram also suggests how the circuits can be divided between the target itself and a download dongle. Instead, it is indirectly addressed through the Special Function Registers. When nothing is connected to the RS connector R1 keeps the 16f input high, which causes the loader to start the application when a reset occurs.

HVP is always available.