Freescale Semiconductor MC68HC08KH12 - Manual (Page 150)

Advance Information MC68HC(7)08KH12 — Rev. 1.1
150 Freescale Semiconductor
10.3 Features
Features of the monitor ROM include the following:
• 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
• 4800 Baud to 28.8 kBaud Communication with Host Computer
• Execution of Code in RAM or ROM
• OTPROM Programming
10.4 Functional Description
The monitor ROM receives and executes commands from a host
computer.
Figure 10-1 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.