Vocoder Bootstrap - Motorola ASTRO Digital Saber Service Manual

MCU SCI port. Now if the Vpp voltage is raised to 12Vdc required on
the FLASH devices for programming; the circuit comprised of VR208,
Q211, and Q208 will trip supplying Vpp to the FLASH devices U205,
U210, 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 multiplex occurs in the SLIC IV U206,
which must also be properly configured.
The ASTRO Digital SABER radio has an additional asynchronous serial
bus which utilizes RS232 bus protocol. This bus utilizes the UART in
the SLIC IC (U206). It is comprised of RS232_DATA_OUT (15),
RS232_DATA_IN (J201-8), CTSOUT* (J201-14), and RTSIN* (J201-10).
It is a two wire duplex bus used to connect to external data devices.

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 U402,
U403, and U414 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 numbers NTN8250E and NTN8250F). All three of these signals are
on the DSP (U405). MODA and MODB configure the memory map of
the DSP when the DSP reset become 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, will cause
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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