MC68HC05T16 Datasheet, PDF (112/128 Pages) Motorola, Inc – High-density complementary metal oxide semiconductor (HCMOS) microcontroller unit

Table 13-1 Mode Selection
RESET
IRQ
PC2
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.
13.1
User Mode (Normal Operation)
The normal operating mode of the MC68HC05T16/MC68HC705T16 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.
13.2
Self-Check Mode
The MC68HC05T16 self-check mode is for the user to check device functions with an on-chip
self-check program masked at location $FE00 to $FFEF under minimum hardware support. The
hardware is shown in Figure 13-3. Figure 13-2 is the criteria to enter self-check mode, where
PC2’s condition is latched within first two clock cycles after the rising edge of the reset. PC2 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 13-2 lists the LEDs’ on-off patterns and their
corresponding indications.
13
+5 V
PC2
+9 V
IRQ
+5 V
RESET
Figure 13-2 Self-Check Mode Timing
MOTOROLA
13-2
OPERATING MODES
TPG
MC68HC05T16