nRF24E1 Nordic VLSI, nRF24E1 Datasheet - Page 50

• Manufacturer Part Number: nRF24E1
• Description: 2.4Ghz RF Transceiver With Embedded 8051 Compatible Microcontroller And 9 Input, 10 Bit ADC
• Manufacturer: Nordic VLSI

PRODUCT SPECIFICATION
The CPU enters the ISR when INT0_N goes low, then waits for a pulse on
INT0_N. Each time INT0_N is pulsed, the CPU exits the ISR, executes one
program instruction, then re-enters the ISR.
The “TICK” is an interval that is nominally 10ms long. This interval is the unit of
resolution both for the watchdog and the RTC wakeup timer. The LP_OSC clock
source of the “TICK” is very inaccurate, and may vary from 6ms to 30ms depending
on processing, temperature and supply voltage. That means that Watchdog and RTC
may not be used for any accurate timing functions.
The accuracy can be improved by calibrating the TICK value at regular intervals. The
register TICK_DV controls how many LP_OSC periods elapse between each TICK.
The frequency of the LP_OSC (between 1 kHz and 5 kHz) can be measured by timer2
in capture mode with t2ex enabled (EXEN2=1). The signal connected to t2ex has
exactly half the frequency of LP_OSC. The 16-bit difference between two consecutive
captures in SFR-registers{RCAP2H,RCAP2L} is proportional to the LP_OSC period.
For details about timer2 see ch. 10.8.3 and Figure 10-5 : Timer 2 – Timer/Counter
with Capture
TICK is controlled by SFR 0xB5.
Addr
SFR
Table 8-1 : TICK control register - SFR 0xB5
The RTC is a simple 16 bit down counter that produces an interrupt and reloads
automatically when the count reaches zero. This process is initially disabled, and will
be enabled with the first write to the timer latch. Writing the timer latch will always be
followed by a reload of the counter. The counter may be disabled again by writing a
disable opcode to the control register. Both the latch and the counter value may be
read by giving the respective codes in the control register, see description in Table 8-2
Nordic VLSI ASA - Vestre Rosten 81, N-7075 Tiller, Norway - Phone [phone] - Fax [phone]
Revision: 1.0
B5
R/W #bit
R/W
8
Init
hex
1D
Name
TICK_DV
QhtrÃ$ÂsÃ(&
Function
Divider that’s used in generating TICK
from LP_OSC frequency.
f
The default value gives a TICK of 10ms
nominal as default.
TICK
= f
LP_OSC
/ (1 + TICK_DV)
July 2003