MC68HC705BD3 FREESCALE [Freescale Semiconductor, Inc], MC68HC705BD3 Datasheet - Page 90

• Manufacturer Part Number: MC68HC705BD3
• Description: High-density complementary metal oxide semiconductor (HCMOS) microcontroller unit
• Manufacturer: FREESCALE [Freescale Semiconductor, Inc]

11
11.1
The normal operating mode of the MC68HC05BD3/MC68HC05BD5/ MC68HC705BD3 is the user
mode. The user mode will be entered if the RESET line is brought low, and the IRQ pin is within
its normal operational range (V
enter the user mode.
11.2
The self-check mode is provided on the MC68HC05BD3 and MC68HC05BD5 for the user to
check device functions with an on-chip self-check program masked at location $3F00 to $3FDF
under minimum hardware support. The hardware is shown in Figure 11-3. Figure 11-2 is the
criteria to enter self-check mode, where PB5’s condition is latched within first two clock cycles after
the rising edge of the reset. PB5 can then be used for other purposes. After entering the self-check
mode, CPU branches to the self-check program and carries out the self-check. Self-check is a
repetitive test, i.e. if all parts are checked to be good, the CPU will repeat the self-check again.
Therefore, the LEDs attached to Port B will be flashing if the device is good; else the combination
of LEDs’ on-off pattern can show what part of the device is suspected to be bad. Table 11-2 lists
the LEDs’ on-off patterns and their corresponding indications.
11-2
RESET
PB5
IRQ
+5V
+9V
+5V
* Minimum hold time should be 2 clock cycles, after that it can be used as a normal IRQ
User Mode (Normal Operation)
Self-Check Mode
function pin.
RESET
5V
5V
Figure 11-2 Self-Check Mode Timing
9V
SS
Table 11-1 Mode Selection
V
to V
+9V Rising Edge*
SS
IRQ
OPERATING MODES
to V
DD
DD
), the rising edge of the RESET will cause the MCU to
V
SS
PB5
V
to V
DD
DD
SELF-CHECK/
BOOTSTRAP
MODE
USER
MC68HC05BD3
TPG