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Controller
Bootstrap and
Asynchronous Buses
The SB9600 bus is an asynchronous serial communications bus
utilizing a Motorola proprietary protocol. Its purpose is a means for
the MCU to communicate with other hardware devices. In the ASTRO
Digital SABER radio, it communicates with hardware accessories
connected to the universal connector.
The SB9600 bus utilizes the UART internal to the MCU operating at
9600 baud. The SB9600 bus consists of a LH_DATA (J201-4) and
SB9600_BUSY (J201-6) signals. LH_DATA is actually the SCI TXD and
RXD ports (U204 - PD0 and PD1) tied together through the MUX U208
(see Figure 8). This makes the bus a simplex single-wire system.
SB9600_BUSY (U204 - PA3) is an active low signal, which is pulled low
when a device wants control of the bus.
The same UART internal to the MCU is used in the controller bootstrap
mode of operation. This mode is used primarily in downloading new
program code to the FLASH ROMs on the VOCON board. In this mode,
the MCU accepts special code downloaded at 7200 baud through the
SCI bus instead of operating from program code resident in its ROMs.
It however must operate in a two wire duplex configuration.
A voltage applied to J201-13 (Vpp) of greater than 10 Vdc will trip the
circuit consisting of Q203, Q204, and VR207. This circuit sets the
MODA and MODB pins of the MCU to bootstrap mode (logic 0,0) and
configures the MUX, U208 to separate the RXD and TXD signals of the
Figure 8 . Host SB9600 and RS232 Ports
PD1 (TXD)
PD0 (RXD)
HC11F1
U204
SLIC IV
U206
U208
J201-4
LH_DATA/BOOT_DATA_OUT
J201-15
RS232_DATA_OUT/BOOT_DATA_IN
BOOT_DATA_IN
BOOT_DATA_OUT
J201-15
SB9600_BUSY
PA3
J201-10
RTS_IN*
J201-8
RS232_DATA_IN
J201-14
CTSOUT*
RXDIN
PJ3
RTSBIN
SLIC IV
U206
MAEPF-24341-O
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