PIC16C71-04/P Microchip Technology Inc., PIC16C71-04/P Datasheet - Page 33

• Manufacturer Part Number: PIC16C71-04/P
• Description: 18 PIN, 1.75 KB OTP, 36 RAM, 13 I/O
• Manufacturer: Microchip Technology Inc.

Specifications of PIC16C71-04/P

• A/d Inputs: 4-Channel, 8-Bit
• Cpu Speed: 5 MIPS
• Eeprom Memory: 0 Bytes
• Input Output: 13
• Memory Type: OTP
• Number Of Bits: 8
• Package Type: 18-pin PDIP
• Programmable Memory: 1.75K Bytes
• Ram Size: 36 Bytes
• Speed: 20 MHz
• Timers: 1-8-bit
• Voltage, Range: 3-6 V
• Lead Free Status / Rohs Status: RoHS Compliant part Electrostatic Device

6.2
When an external clock input is used for Timer0, it must
meet certain requirements. The requirements ensure
the external clock can be synchronized with the internal
phase clock (T
incrementing of Timer0 after synchronization.
6.2.1
When no prescaler is used, the external clock input is
the same as the prescaler output. The synchronization
of T0CKI with the internal phase clocks is accom-
plished by sampling the prescaler output on the Q2 and
Q4 cycles of the internal phase clocks (Figure 6-5).
Therefore, it is necessary for T0CKI to be high for at
least 2Tosc (and a small RC delay of 20 ns) and low for
at least 2Tosc (and a small RC delay of 20 ns). Refer to
the electrical specification of the desired device.
When a prescaler is used, the external clock input is
divided by the asynchronous ripple-counter type pres-
FIGURE 6-5:
1997 Microchip Technology Inc.
Note 1: Delay from clock input change to Timer0 increment is 3Tosc to 7Tosc. (Duration of Q = Tosc).
Using Timer0 with an External Clock
EXTERNAL CLOCK SYNCHRONIZATION
2: External clock if no prescaler selected, Prescaler output otherwise.
3: The arrows indicate the points in time where sampling occurs.
External Clock/Prescaler
Output after sampling
External Clock Input or
Prescaler output
Therefore, the error in measuring the interval between two edges on Timer0 input = 4Tosc max.
Increment Timer0 (Q4)
OSC
TIMER0 TIMING WITH EXTERNAL CLOCK
). Also, there is a delay in the actual
(2)
Timer0
Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4
(3)
(1)
T0
caler so that the prescaler output is symmetrical. For
the external clock to meet the sampling requirement,
the ripple-counter must be taken into account. There-
fore, it is necessary for T0CKI to have a period of at
least 4Tosc (and a small RC delay of 40 ns) divided by
the prescaler value. The only requirement on T0CKI
high and low time is that they do not violate the mini-
mum pulse width requirement of 10 ns. Refer to param-
eters 40, 41 and 42 in the electrical specification of the
desired device.
6.2.2
Since the prescaler output is synchronized with the
internal clocks, there is a small delay from the time the
external clock edge occurs to the time the Timer0 mod-
ule is actually incremented. Figure 6-5 shows the delay
from the external clock edge to the timer incrementing.
TMR0 INCREMENT DELAY
T0 + 1
PIC16C71X
T0 + 2
Small pulse
misses sampling
DS30272A-page 33