Motorola MC68HC908AB32 User Manual

Monitor ROM (MON)
Technical Data MC68HC908AB32 — Rev. 1.0
160 Monitor ROM (MON) MOTOROLA
10.4.1 Entering Monitor Mode
Table 10-1 shows the pin conditions for entering monitor mode.
Enter monitor mode by either
• Executing a software interrupt instruction (SWI) or
• Applying a logic 0 and then a logic 1 to the RST
pin.
The MCU sends a break signal (10 consecutive logic 0s) to the host
computer, indicating that it is ready to receive a command. The break
signal also provides a timing reference to allow the host to determine the
necessary baud rate.
Monitor mode uses alternate vectors for reset, SWI, and break interrupt.
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 V
TST
(see Section 23. Electrical Specifications) is applied to either the IRQ
pin or the RST
pin. (See Section 8. System Integration Module (SIM)
for more information on modes of operation.)
NOTE: Holding the PTC3 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% duty cycle at maximum bus frequency.
Table 10-1. Monitor Mode Entry Conditions
IRQ Pin
PTC0 Pin PTC1 Pin PTA0 Pin PTC3 Pin
CGMOUT
Bus Frequency
(CGMOUT ÷ 2)
V
TST
(1)
Notes:
1. For V
TST
, see Section 23. Electrical Specifications.
1011
CGMXCLK ÷ 2
or
CGMVCLK ÷ 2
CGMXCLK ÷ 4
or
CGMVCLK ÷ 4
V
TST
1010 CGMXCLK CGMXCLK ÷ 2

Motorola MC68HC908AB32 Specifications

General

Brand	Motorola
Model	MC68HC908AB32
Category	Controller
Language	English