Development Support
Monitor Module (MON)
MC68HC08GP32A MC68HC08GP16A
Data Sheet
MOTOROLA
Development Support
251
19.3.1 Functional Description
Figure 19-8 shows a simplified diagram of monitor mode entry.
The monitor module receives and executes commands from a host computer.
Figure 19-9 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.
19.3.1.1 Monitor Mode Entry
Table 19-2 shows the pin conditions for entering monitor mode. As specified in the
table, monitor mode may be entered after a power-on reset (POR) and will allow
communication provided the pin and clock conditions are met.
The rising edge of the internal RST signal latches the monitor mode. Once monitor
mode is latched, the values on PTA7, PTC0, PTC1, and PTC3 pins can be
changed.
Once out of reset, the MCU waits for the host to send eight security bytes
(see 19.3.2 Security). After the security bytes, the MCU sends a break signal
(10 consecutive 0s) to the host, indicating that it is ready to receive a command.
19.3.1.2 Monitor Vectors
In monitor mode, the MCU uses different vectors for reset, SWI (software interrupt),
and break interrupt than those for user mode. The alternate vectors are in the $FE
page instead of the $FF page and allow code execution from the internal monitor
firmware instead of user code. The COP module is disabled in monitor mode as
long as VTST is applied to either the IRQ pin or the RST pin.
Table 19-1 summarizes the differences between user mode and monitor mode
regarding vectors.
Table 19-1. Mode Differences
Modes
Functions
COP
Reset
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 (VTST) is removed from the IRQ pin while in monitor mode, the SIM asserts
its COP enable output. The COP is a mask option enabled or disabled by the COPD bit in the
$FEFE
$FEFF
$FEFC
$FEFD
$FEFC
$FEFD