NM95HS01 NSC [National Semiconductor], NM95HS01 Datasheet - Page 10

• Manufacturer Part Number: NM95HS01
• Description: HiSeC-TM High Security Rolling Code Generator
• Manufacturer: NSC [National Semiconductor]

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Data Frame Fields
TRANSMISSION INDICATION
Both the LED and RFEN signals can be used to indicate
HiSeC rolling code transmission The LED output is active
low during the transmission of a pause whereas the RFEN
output is active low during transmission of either a frame or
a pause Either output may be used to provide a visual indi-
cation of transmission by connecting an LED between V
and LED or RFEN
If the low battery detect option is enabled and the battery is
low the LED output is active only during the pause following
the first frame of a new code transmission It is not active on
successive pauses in order to conserve power
Operational Timing Issues
DATA FRAME PAUSE LENGTH
After the complete transmission of a data frame a pause is
inserted before the next data frame is transmitted The
pause length can be modifed by configuring the 2-bit Pause-
Length parameter in EEPR0M PauseLength is broken down
into two single bit parameters Pause1 and Pause0 Avail-
able configuration options are shown in Table III
HiSeC GENERATOR TIME-OUT
If
(TIMEOUTEN
onds after a key is first activated regardless of whether the
key is still being pressed This option guards against the
condition that a key may be stuck low which could drain the
battery If TIMEOUTEN
transmit data frames as long as a key is pressed
PAUSE1
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the
0
0
1
1
TABLE III Pause Length Select Options
NM95HS01 02
PAUSE0
e
1) the device will enter halt mode 80 sec-
0
1
0
1
e
20
50
0 the generator will continue to
0
8
time-out
Function
c
c
c
c
(Continued)
P3 Output
P3 Output
P3 Output
P3 Output
option
FIGURE 9 NM95HS01 02 Timer Block Example
FIGURE 8 The NM95HS01 02 Timer Block
Pause Time
No Pause
is
100 ms
20 ms
50 ms
enabled
CC
10
Figure 9 provides the basis for an example in calculating the
HiSeC GENERATOR TIMER BLOCK
Bit timing and several function operating times are set in the
generator through a user programmable timer block This
timer block is used to provide IR and RF bit timing signals
the interframe pause time the AutoResync timing period
and the time-out delay
The NM95HS01 02 timer block consists of three program-
mable 6-bit prescalers and a fixed 16-bit prescaler The in-
put to Prescaler1 is
the IR clock This signal becomes the input to Prescaler2
The output from Prescaler2 is the RF clock This signal then
becomes the input to Prescaler3 The output from Prescal-
er3 is a target value of 2 5 ms Finally this 2 5 ms timing
signal becomes the input to the fixed 16-bit prescaler There
are several outputs from this prescaler The 2 5 ms is divid-
ed by 4 4096 and 32768 and these times are used to set
the key debounce time (10 ms) the AutoResync time
(
respectively
The NM95HS01 02 timer block is shown in Figure 8
The purpose of the prescalers is to provide various timing
signals to the state machines in the generator The IR clock
is used as a time base for the various IR bit coding formats
The RF clock is used for RF bit coding formats A program-
mable bit called SCLK determines whether the IR clock
(SCLK
timing time base In addition to SCLK the system designer
can program Prescaler1 Prescaler2 and Prescaler3 sepa-
rately to set the necessary division factors Since each of
these prescalers is 6 bits permissible values range from 2
to 64
The system designer must set the programmable prescalers
to meet the necessary timing requirements for all the func-
tions discussed above All of these timings are interdepen-
dent
necessary timing for these functions and setting the timer
block appropriately
l
10 sec) and the generator time-out period (
e
0) or the RF clock (SCLK
of the frequency of CKI The output is
TL D 12302 – 20
e
TL D 12302– 19
1) is used as the bit
l
80 sec)