3-52 Theory of Operation: Controller
3.2.7.1 MACE IC
The encryption module uses the MACE IC and an encryption key variable to perform its encode/
decode function. The encryption key variable is loaded into the MACE IC, via the GCAI (side)
connector, from a hand-held, key variable loader (KVL). The MACE IC contains the particular
encryption algorithm purchased.
Once the MACE IC has its encryption keys and algorithm, it communicates with the radio' s host
processor (OMAP) through the Synchronous Serial Interface (SSI) bus. Both commands and audio
(clear and encrypted) are sent through the SSI bus. A communications failure between the host
processor and the secure module will be indicated as an ERROR 09/10 message on the display.
Figure 3-10 below lists the corresponding kit numbers.
The MACE IC relies on a 4 MHz clock source provided by the CPLD, the clock is connected to
MACE's XIN pin (U2510-P5).
3.2.7.2 Key Loading / Fail
Key variables are loaded into the MACE IC through the keyfail line. The signal originates from the
GCAI connector (pin 11 of J2 on the Front kit flex) and is passed through the keypad board to the
main board. The signal is then selected by a multiplexer (U4003) controlled by CPLD output,
KEYFAIL_CTRL, and the signal is routed back to the keypad board to the MACE's KYLD pin
(U2510-B10).
3.2.7.3 Key Retention
The key variables are retained within the MACE IC's memory (SRAM or FLASH). The keys can be
infinite key retention or 30-seconds key retention, depending on how the codeplug is set up. When
set to infinite key retention, the keys are stored in the FLASH memory inside the MACE IC. When set
to 30-second retention, the keys are stored in SRAM, and will be erased when the radio's battery is
removed (after the 30 second delay). The key retention delay circuit controls this time through a
comparator op-amp circuit (U2526). When the battery is removed, VSAVE (nominally 2.5 V) will
eventually drop to 0V after 30 seconds, which will result in a 0V output from U2526. This output is the
input to the CONT_1.875 regulator (U2525), which is nominally 3.3 V. When the regulator's output is
0 V, the keys in MACE's SRAM will be erased.
3.2.7.4 Tamper
The tamper function is intended to erase the encryption keys in a tampering situation. If the radio
chassis is opened during operation, the tamper signal, which is normally connected to ground
through spring contact M2533, will be disconnected from ground. This will be sensed by MACE
through its tamper pin TPR0 (U2510-M2). Once this condition is sensed, the encryption keys will be
erased.
Table 3-10. Secure Keypad KIT Numbers
KIT Number Description
PMCN4028_ APX 2000/ APX 4000 Expanded Limited Keypad Board
PMCN4026_ APX 2000/ APX 4000 Expanded Full Keypad Board
PMCN4048_ APX 2000/ APX 4000 (Two Knobs) Keypad Board Model 2
PMCN4029_ APX 2000/ APX 4000 (Two Knobs) Keypad Board Model 3
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