MC68HC05B6_13 Datasheet, PDF (55/302 Pages) Freescale Semiconductor, Inc – Microcontrollers

4.3
Port C
In addition to the standard port functions described for port A and B, port C pin 2 can be
configured, using the ECLK bit of the EEPROM/ECLK control register, to output the CPU clock. If
this is selected the corresponding DDR bit is automatically set and bit 2 of port C will always read
the output data latch. The other port C pins are not affected by this feature.
EEPROM/ECLK control
Address bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
State
on reset
$0007 0
0
0
0 ECLK E1ERA E1LAT E1PGM 0000 0000
4
ECLK — External clock output bit
1 (set) – ECLK CPU clock is output on PC2.
0 (clear) – ECLK CPU clock is not output on PC2; port C acts as a normal I/O port.
The ECLK bit is cleared by power-on or external reset. It is not affected by the execution of a STOP
or WAIT instruction.
The timing diagram of the clock output is shown in Figure 4-2.
Internal clock (PHI2)
External clock (ECLK/PC2)
Output port (if write to output port)
Figure 4-2 ECLK timing diagram
4.4
Port D
This 8-bit input-only port shares its pins with the A/D converter subsystem. When the A/D
converter is enabled, pins PD0-PD7 read the eight analog inputs to the A/D converter. Port D can
be read at any time, however, if it is read during an A/D conversion sequence noise, may be
injected on the analog inputs, resulting in reduced accuracy of the A/D. Furthermore, performing
MC68HC05B6
Rev. 4.1
INPUT/OUTPUT PORTS
Freescale
4-3