MC908GR8CDWE Datasheet, PDF (190/408 Pages) Freescale Semiconductor, Inc – M68HC08 Microcontrollers

Freescale Semiconductor, Inc.
Monitor ROM (MON)
• FLASH memory security feature⁽¹⁾
• FLASH memory programming interface
• Enhanced PLL (phase-locked loop) option to allow use of external
32.768-kHz crystal to generate internal frequency of 2.4576 MHz
• 310 byte monitor ROM code size ($FE20 to $FF55)
• Monitor mode entry without high voltage, V_TST, if reset vector is
blank ($FFFE and $FFFF contain $FF)
• Standard monitor mode entry if high voltage, V_TST, is applied to
IRQ
15.4 Functional Description
The monitor ROM receives and executes commands from a host
computer. Figure 15-1 shows an example 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 code downloaded into RAM by a host
computer while most 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 pullup resistor.
Technical Data
190
1. No security feature is absolutely secure. However, Motorola’s strategy is to make reading or
copying the FLASH difficult for unauthorized users.
MC68HC908GR8 — Rev 4.0
Monitor ROM (MON)
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA