Freescale Semiconductor MC68HC908MR32 - Manual (Page 256)

Development Support
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1
256 Freescale Semiconductor
Features 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
• 4800 baud–28.8 Kbaud communication with host computer
• Execution of code in random-access memory (RAM) or ROM
• FLASH programming
18.3.1 Functional Description
The monitor ROM receives and executes commands from a host computer. Figure 18-8 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 pullup resistor.
18.3.1.1 Entering Monitor Mode
There are two methods for entering monitor:
• The first is the traditional M68HC08 method where V
DD
+ V
HI
is applied to IRQ1 and the mode pins
are configured appropriately.
• A second method, intended for in-circuit programming applications, will force entry into monitor
mode without requiring high voltage on the IRQ1 pin when the reset vector locations of the FLASH
are erased ($FF).
NOTE
For both methods, holding the PTC2 pin low when entering monitor mode
causes a bypass of a divide-by-two stage at the oscillator. The CGMOUT
frequency is equal to the CGMXCLK frequency, and the OSC1 input
directly generates internal bus clocks. In this case, the OSC1 signal must
have a 50 percent duty cycle at maximum bus frequency.
Table 18-1 is a summary of the differences between user mode and monitor mode.
18.3.1.2 Normal Monitor Mode
Table 18-2 shows the pin conditions for entering monitor mode.
Table 18-1. Mode Differences
Modes
Functions
COP
Rest
Vector High
Reset
Vector Low
Break
Vector High
Break
Vector Low
SWI
Vector High
SWI
Vector Low
User Enabled $FFFE $FFFF $FFFC $FFFD $FFFC $FFFD
Monitor Disabled
(1)
1. If the high voltage (V
DD
+ V
HI
) is removed from the IRQ1 pin or the RST pin, the SIM asserts its COP enable output. The
COP is a mask option enabled or disabled by the COPD bit in the configuration register.
$FEFE $FEFF $FEFC $FEFD $FEFC $FEFD