SLOS787H – MAY 2012 – REVISED APRIL 2014
6.13.3.2.8 Modulator and SYS_CLK Control Register (0x09)
The frequency of SYS_CLK (pin 27) is programmable by the bits B4 and B5 of this register. The frequency
of the TRF7964A system clock oscillator is divided by 1, 2 or 4 resulting in available SYS_CLK
frequencies of 13.56 MHz or 6.78 MHz or 3.39 MHz.
The ASK modulation depth is controlled by bits B0, B1 and B2. The range of ASK modulation is 7% to
30% or 100% (OOK). The selection between ASK and OOK (100%) modulation can also be done using
direct input OOK (pin 12). The direct control of OOK/ASK using OOK pin is only possible if the function is
enabled by setting B6 = 1 (en_ook_p) in this register (0x09) and the ISO Control Register (0x01, B6 = 1).
When configured this way, the MOD (pin 14) is used as input for the modulation signal.
Table 6-30. Modulator and SYS_CLK Control Register (0x09)
Function:
Controls the modulation input and depth, ASK / OOK control and clock output to external system (MCU)
Default:
0x91 at POR = H or EN = L, and at each write to ISO control register, except Clo1 and Clo0.
Bit
Name
Function
Description
B7
27MHz
Enables 27.12-MHz crystal
Default = 1 (enabled)
Enable ASK/OOK pin (pin 12) for "on the fly change" between any preselected
1 = Enables external
ASK modulation as defined by B0 to B2 and OOK modulation:
selection of ASK or OOK
B6
en_ook_p
modulation
If B6 is 1, pin 12 is configured as follows:
0 = Default operation as
1 = OOK modulation
defined in B0 to B2 (0x09)
0 = Modulation as defined in B0 to B2 (0x09)
SYS_CLK Output SYS_CLK Output
Clo1
Clo0
(if 13.56-MHz
(if 27.12-MHz
SYS_CLK output frequency
crystal is used)
crystal is used)
B5
Clo1
MSB
0
0
Disabled
Disabled
0
1
3.39 MHz
6.78 MHz
1
0
6.78 MHz
13.56 MHz
SYS_CLK output frequency
B4
Clo0
LSB
1
1
13.56 MHz
27.12 MHz
1 = Sets pin 12 (ASK/OOK)
For test and measurement purpose. ASK/OOK pin 12 can be used to monitor
B3
en_ana
as an analog output
the analog subcarrier signal before the digitizing with DC level equal to AGND.
0 = Default
Pm2
Pm1
Pm0
Mod Type and %
B2
Pm2
Modulation depth MSB
0
0
0
ASK 10%
0
0
1
OOK (100%)
0
1
0
ASK 7%
B1
Pm1
Modulation depth
0
1
1
ASK 8.5%
1
0
0
ASK 13%
1
0
1
ASK 16%
B0
Pm0
Modulation depth LSB
1
1
0
ASK 22%
1
1
1
ASK 30%
58
Detailed Description
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