Motorola MC68VZ328 Chapter 17 Bootstrap Mode

Bootstrap Mode 17-1

Chapter 17Bootstrap Mode

This chapter describes the operation and programming information of the bootstrap mode of the

MC68VZ328. The bootstrap mode is designed to allow the initialization of a target system and the ability

to download programs or data to the target system RAM using either the UART1 or UART 2 controller.

See Chapter14, “Universal Asynchronous Receiver/Transmitter 1 and 2,” for information on operating

and programming the UART controllers. Once a program is downloaded to the MC68VZ328, it can be

executed, providing a simple debugging environment for failure analysis and a channel to update pr ograms

stored in flash memory. The features of bootstrap mode are as follows:

• Allows system initialization and the ability to download both programs and data to syst em memory

using UART1 or UART 2

• Accepts execution commands to run programs stored in system memory

• Provides a 32-byte instruction buffer for 68000 instruction storage and execution

In bootstrap mode, the MC68VZ328’s UART1 and UART 2 controllers are initialized to 19,200 baud, no

parity, 8-bit character, and 1 stop bit, and then they are ready to accept bootstrap data download. The first

character received is used to instruct the MC68VZ328 whether the PLL input clock is 32.768 kHz or

38.4 kHz crystal, as well as to determine which UART port is being used for bootstrapping. The first

character can be any value and is not part of the program or data being downloaded. Downloading the data

or program requires the user convert the code to a bootstrap format file, which is a text file that contains

bootstrap records. A DOS-executable program, STOB.EXE, can be downloaded from the DragonBall Web

site (http://www.Motorola.com/DragonBall) to convert an S-record file to a bootstrap format file.

Before a program is downloaded to system memory, the MC68VZ328’s internal registers should be set to

initialize the target system. Since internal registers are treated as a type of memory, each of them can be

initialized by issuing a bootstrap record.

The bootstrap design provides a 32-byte instruction buffer to which 68000 instructions may be

downloaded. This feature enables the 68000 instructions to execute even if the memory systems are

disabled or the MC68VZ328 is operating in a CPU standalone system. The instruction buffer starts at

0xFFFFC0. Whether initializing internal registers, downloading a program to system RAM, or issuing a

core instruction, bootstrap mode will only accept bootstrap record transfers that are made usi ng the UART.

The record type determines what occurs.