Technical Manual

6-10
Controller
Bootstrap and
Asynchronous Buses
The SB9600 bus is an asynchronous serial communications bus
utilizing a Motorola proprietary protocol. It provides a means for the
MCU to communicate with other hardware devices. In the ASTRO
Digital XTS 3000 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 LH_DATA (J101-2) and
SB9600_BUSY (J101-8) signals. LH_DATA is actually the SCI TXD and
RXD ports (U701 — PD0 and PD1) tied together through the MUX
U704 (see Figure 11). This makes the bus a simplex, single-wire system.
SB9600_BUSY (U701 — PA3) is an active low signal that 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 vocoder and controller
boards. In this mode, the MCU accepts special code, downloaded at
7200 baud via the SCI bus, instead of operating from program code
resident in its ROMs. However, it must operate in a two-wire, duplex
configuration.
A voltage applied to J101-12 (Vpp) of greater than 10 Vdc will trip the
circuit consisting of Q104, and VR119. This circuit sets the MODA and
+5V
D101
BOOT_DATA-OUT
BOOT_DATA_IN
KEYFAIL*
J101-8
SB9600_BUSY
J101-2
LH_DATA/BOOT_DATA_OUT/
KEYFAIL*
J101-6
RS232_DATA_OUT/
BOOT_DATA_IN
J101-4
RS232_DATA_IN
J101-1
CTS_OUT*
U717
U704
PA3
HC11F1
U701
PDØ (RXD)
Encryption
Module
J601-15
PDI (TXD)
J101-10
RTSIN*
BOOTRX
PJ2
PH4
RXDIN
SLIC V
U702
PJ3
RTSBIN
MAEPF-26003-O
Figure 11 Host SB9600 and RS232 Ports