MC68HC05BD3 Datasheet, PDF (90/112 Pages) Motorola, Inc – HCMOS microcontroller

Table 11-1 Mode Selection
RESET
IRQ
PB5
MODE
5V
V_SS to V_DD
V_SS to V_DD
USER
5V
9V
+9V Rising Edge*
V_DD
SELF-CHECK/
BOOTSTRAP
* Minimum hold time should be 2 clock cycles, after that it can be used as a normal IRQ
function pin.
11.1
User Mode (Normal Operation)
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_SS to V_DD), the rising edge of the RESET will cause the MCU to
enter the user mode.
11.2
Self-Check Mode
11
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.
+5 V
PB5
+9 V
IRQ
+5 V
RESET
MOTOROLA
11-2
Figure 11-2 Self-Check Mode Timing
OPERATING MODES
TPG
MC68HC05BD3