3.2 Program/Verify Commands

Once a device has entered ICSP Program/Verify mode (using either high-voltage or LVP entry), the programming host device may issue commands to the microcontroller, each eight bits in length. The commands are summarized in Table 3-1 and are used to erase or program the device based on the location of the Program Counter (PC).

Some 8-bit commands also have an associated data payload (such as Load PC Address and Read Data from NVM).

If the host device issues an 8-bit command byte that has an associated data payload, the host device is responsible for sending an additional 24 clock pulses (e.g., three 8-bit bytes) to send or receive the payload data associated with the command.

The payload field size is compatible with many 8-bit SPI-based systems. Within each 24-bit payload field, the first bit transmitted is always a Start bit, followed by a variable number of Pad bits, followed by the useful data payload bits and ending with one Stop bit. The useful data payload bits are always transmitted MSb first.

When the programming device issues a command that involves a host to the microcontroller payload (e.g., Load PC Address), the Start, Stop and Pad bits must all be driven by the programmer, as defined by the data column in Table 3-1. When the programming host device issues a command that involves the microcontroller to host payload data (e.g., Read Data from NVM), the Start, Stop and Pad bits must be treated as ‘don't care’ bits and the values may be ignored by the host.

When the programming host device issues an 8-bit command byte to the microcontroller, the host must wait a specified minimum amount of delay (which is command-specific) prior to sending any additional clock pulses (associated with either a 24-bit data payload field or the next command byte).