mc68hc05bs8 Freescale Semiconductor, Inc, mc68hc05bs8 Datasheet - Page 108

• Manufacturer Part Number: mc68hc05bs8
• Description: Mc68hc05 Family Of Low-cost Single-chip Microcontrollers.
• Manufacturer: Freescale Semiconductor, Inc

12
12.1
The normal operating mode of the MC68HC05BS8/ MC68HC705BS8 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
mode.
12.2
The self-check mode is provided on the MC68HC05BS8 for the user to check device functions with
an on-chip self-check program masked at location $1600 to $17FF under minimum hardware
support. The self-check schematic is shown in Figure 12-3. Figure 12-2 is the criteria to enter
self-check mode, where PB6’s condition is latched within first two clock cycles after the rising edge
of the reset. PB6 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 A 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 12-2 lists the LEDs’ on-off
patterns and their corresponding indications.
12-2
RESET
PB6
IRQ
* Minimum hold time should be 2 clock cycles, after that it can be used as a normal IRQ function pin.
+5V
+9V
+5V
User Mode (Normal Operation)
Self-Check Mode
RESET
5V
5V
SS
to V
DD
Figure 12-2 Self-Check Mode Timing
9V
), the rising edge of the RESET will cause the MCU to enter the user
V
Table 12-1 Mode Selection
+9V Rising Edge*
SS
IRQ
to V
OPERATING MODES
DD
V
SS
PB6
V
to V
DD
DD
SELF-CHECK/
BOOTSTRAP
MODE
USER
MC68HC05BS8
TPG