Vocoder Bootstrap - Motorola ASTRO XTS 3000 Service Manual

the MUX (U704) to separate the RXD and TXD signals of the MCU SCI
port. Now, if the Vpp voltage is raised to 12Vdc required on the FLASH
devices for programming, the circuit comprising VR121, Q109, and
Q110 will trip supplying Vpp to the FLASH devices U727 and U404.
One more complication exists in that the BOOT_DATA_IN signal
(RXD) is multiplexed with the RS232 data out signal
RS232_DATA_OUT. This multiplexing occurs in the SLIC IV (U702),
which must also be properly configured.
The ASTRO Digital XTS 3000 radio has an additional asynchronous
serial bus which utilizes RS232 bus protocol. This bus utilizes the UART
in the SLIC IC (U702). It consists of RS232_DATA_OUT (J101-6),
RS232_DATA_IN (J101-4), CTSOUT* (J101-1), and RTSIN* (J101-10). It
is a two-wire duplex bus, used to connect to external data devices. This
bus is used to keyload radios equipped with encryption modules.
When keyloading a radio, the RS232_DIN* and CTSOUT* lines are
pulled low by the keyloader, and MUX U717 will be enabled by the
MCU. The keyloading data (multiplexed with the LH_DATA/
BOOT_DATA_OUT line) is sent to the encryption module on the
KEYFAIL* line. This data will be ignored at the MCU's PDI port.

Vocoder Bootstrap

The DSP has two modes of bootstrap: from program code stored in the
FLASH ROM (U404), or retrieving code from the host port.
During normal modes of operation, the DSP executes program code
stored in the FLASH ROM, U404. Unlike the MCU, however, the DSP
moves the code from the FLASH ROM into the three SRAMs (U401,
U402, and U403), where it is executed from. Since, at initial start-up,
the DSP must execute this process before it can begin to execute
system code, it is considered a bootstrap process. In this process, the
DSP fetches 512 words, 1536 bytes, of code from the FLASH ROM,
starting at physical address $C000, and moves it into internal P
memory. This code contains the system vectors, including the reset
vector. It then executes this piece of bootstrap code, which basically in
turn moves additional code into the external SRAMs.
A second mode of bootstrap allows the DSP to load this initial 512
words of data from the host port, being supplied by the MCU. This
mode is used for FLASH programming the DSP ROM when the ROM
may initially be blank. In addition, this mode may be used for
downloading some diagnostic software for evaluating that portion of
the board.
The bootstrap mode for the DSP is controlled by three signals: MODA/
IRQA*, MODB/IRQB*, and D23 (kit number NTN8250D), or MODC
(kit number NTN8250E). All three of these signals are on the DSP
(U405). MODA and MODB configure the memory map of the DSP
when the DSP reset becomes active. These two signals are controlled
by the ADSIC (U406) during power-up, which sets MODA low and
MODB high for proper configuration. Later, these lines become
interrupts for analog signal processing. D23/MODC controls whether
the DSP will look for code from the MCU or will retrieve code from the
FLASH ROM. D23 high, or MODC low out of reset, causes the DSP to
seek code from the FLASH ROM (U404). For the second mode of
bootstrap, the MCU drives BOOTMODE low, causing D23 to go low
and MODC to go high.
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