MC68HC08BD24 Datasheet, PDF (106/244 Pages) Motorola, Inc – HCMOS Microcontroller Unit

9.3 Features
Features of the monitor ROM include:
• Normal user-mode pin functionality
• One pin dedicated to serial communication between monitor ROM
and host computer
• Standard mark/space non-return-to-zero (NRZ) communication
with host computer
• 9600 Baud communication with host computer
• Execution of code in RAM
9.4 Functional Description
The monitor ROM receives and executes commands from a host
computer. Figure 9-1 shows a sample circuit used to enter monitor
mode and communicate with a host computer via a standard RS-232
interface.
Simple monitor commands can access any memory address. In monitor
mode, the MCU can execute host-computer code in RAM while all MCU
pins retain normal operating mode functions. All communication
between the host computer and the MCU is through the PTA0 pin. A
level-shifting and multiplexing interface is required between PTA0 and
the host computer. PTA0 is used in a wired-OR configuration and
requires a pull-up resistor.
Technical Data
106
MC68HC08BD24 — Rev. 1.1
Freescale Semiconductor