EM78P156E
VI.3 TCC/WDT & Prescaler
There is an 8-bit counter available as prescaler for the TCC or WDT. The prescaler is available for the TCC only
or the WDT only at the same time and the PAB bit of the CONT register is used to determine the prescaler assigment.
The PSR0~PSR2 bits determine the ratio. The prescaler will be cleared by the instructions which write to TCC each time,
when assigned to TCC mode. The WDT and prescaler, when assigned to WDT mode, will be cleared by the “WDTC”
and “SLEP” instructions. Fig.5 depicts the circuit diagram of TCC/WDT.
• R1 (TCC) is an 8-bit timer/counter. The clock source of TCC can be internal clock or external clock input (edge
selectable from TCC pin). If TCC signal source is from internal clock, TCC will increase by 1 in every instruction
cycle (without prescaler). Refer to Fig.5, CLK=Fosc/2 or CLK=Fosc/4 is depended on the CODE option bit CLKS.
CLK=Fosc/2 if CLKS bit is “0”, and CLK=Fosc/4 if CLKS bit is “1”. If TCC signal source is from external clock
input, TCC will increase by 1 on every falling edge or rising edge of TCC pin.
• The watchdog timer is a free running on-chip RC oscillator. The WDT will keep running even the oscillator driver
has been turned off (i.e. in sleep mode). During the normal operation or the sleep mode, a WDT time-out (if enabled)
will cause the device to reset. The WDT can be enabled or disabled at any time during the normal mode by software
programming. Refer to WDTE bit of IOCE register. With no presacler, the WDT time-out period is approximately
18 ms.
CLK(Fosc/2 or Fosc/4)
0
Data Bus
1
TCC
Pin
1
M
U
X
0
M
U
X
SYNC
2 cycles
TCC(R1)
TE
TS
PAB
TCC overflow interrupt
0
WDT
1
M
U
X
8-bit Counter
IOCA
PSR0 ~PSR2
PAB
WDTE
(in IOCE)
8-to-1 MUX
0
1
MUX
PAB
WDT time-out
Fig. 5 Block diagram of TCC and WDT
VI.4 I/O Ports
The I/O registers, both Port 5 and Port 6, are bi-directional tri-state I/O ports. Port 6 can be pulled high internally
by software. In addition, Port 6 can also have open-drain output by software. There is an input status changed interrupt
(or wake-up) function on Port 6. P50 ~ P52 and P60 ~ P63 pins can be pulled down by software. Each I/O pin can be
defined as “input” or “output” pin by the I/O control registers (IOC5 ~ IOC6). P50~P51 are the R-option pins enabled
by setting the ROC bit in the IOCE register to 1. While the R-option function is used, P50~P51 are recommended to be
used as output pins. During the period of R-option being enabled, P50~P51 must be programmed as input pins. In the
R-option mode, the current consuming by the Rex should be taken into the consideration, if the low power consumption
is concerned.
* This specification is subject to be changed without notice.
B3-9
8.11.1999
EMC [ ELAN MICROELECTRONICS CORP ]
