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SLOS743L – AUGUST 2011 – REVISED MARCH 2017
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Detailed Description
Copyright © 2011–2017, Texas Instruments Incorporated
6.15.3.2.8 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 TRF7970A 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.
describes the Modulator and SYS_CLK Control register.
Table 6-36. 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)
B6
en_ook_p
1 = Enables external
selection of ASK or OOK
modulation
0 = Default operation as
defined in B0 to B2 (0x09)
Enable ASK/OOK pin (pin 12) for "on the fly change" between any preselected
ASK modulation as defined by B0 to B2 and OOK modulation:
If B6 is 1, pin 12 is configured as follows:
1 = OOK modulation
0 = Modulation as defined in B0 to B2 (0x09)
B5
Clo1
SYS_CLK output frequency
MSB
Clo1
Clo0
SYS_CLK Output
(if 13.56-MHz
crystal is used)
SYS_CLK Output
(if 27.12-MHz
crystal is used)
0
0
Disabled
Disabled
0
1
3.39 MHz
6.78 MHz
B4
Clo0
SYS_CLK output frequency
LSB
1
0
6.78 MHz
13.56 MHz
1
1
13.56 MHz
27.12 MHz
B3
en_ana
1 = Sets pin 12 (ASK/OOK)
as an analog output
0 = Default
For test and measurement purpose. ASK/OOK pin 12 can be used to monitor
the analog subcarrier signal before the digitizing with DC level equal to AGND.
B2
Pm2
Modulation depth MSB
Pm2
Pm1
Pm0
Mod Type and %
0
0
0
ASK 10%
0
0
1
OOK (100%)
B1
Pm1
Modulation depth
0
1
0
ASK 7%
0
1
1
ASK 8.5%
1
0
0
ASK 13%
B0
Pm0
Modulation depth LSB
1
0
1
ASK 16%
1
1
0
ASK 22%
1
1
1
ASK 30%