Motorola MC68VZ328 - Manual (Page 307)

Bootstrap Mode 17-1
Chapter 17
Bootstrap 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 UART 1 or UART 2 controller.
See Chapter 14, “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 programs
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 system memory
using UART 1 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
17.1 Bootstrap Mode Operation
In bootstrap mode, the MC68VZ328’s UART 1 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 using the UART.
The record type determines what occurs.