Esd Protection Circuitry; Universal Connector (Side Connector) Interface Circuitry - Motorola XTS 2500 Service Manual

700/800 MHz Detailed Theories of Operation: VOCON Functional Blocks
These new accessories are to ground, designator R666, of the side connector. When this occurs, the
ONE_WIRE_OPT is asserted and the dual-core processor detects the change. The dual-core
processor then sends a command through the SPI lines to the U701 MAKO IC to connect the side
connector One-Wire line to the dual-core processor One-Wire bus. In the case of the USB cable, the
dual-core processor reads the One-Wire data from the cable and, upon determining that a USB
cable is attached, programs the digital-support IC for USB mode.
4.4.6.3.1.4 Watchdog Timer
The watchdog timer is a 125ms counter that is integrated into the MAKO IC U701 and used during
the power down sequence. The MAKO IC will begin the power down sequence when a low-to-high
transition occurs on MECH_SW pin (MAKO pin E4). Once this transition occurs, the MAKO IC
begins the watchdog timer. Upon expiration, RESETX (MAKO pin C5) is asserted and all of the
MAKO regulators are shutdown. The dual-core processor can refresh the watchdog timer so that the
software has enough time to complete its tasks before the power is taken away.
4.4.6.3.1.5 32 kHz Oscillator and CMOS Output
There is an internal 32kHz oscillator circuitry to the MAKO IC U701 that is based off of a 32.768 kHz
crystal Y701 and additional load capacitors C701 and C702. The output of the 32 kHz oscillator is a
logic_vdd voltage (approximately 2.9 volts peak-to-peak), 32kHz +/- 20% square wave on pin
GATED_32K_CLK. This 32 kHz signal is routed through an analog switch U712 and sent to the
dual-core processor CKIL pin. This signal is only used to boot up the dual-core processor.
After the dual-core processor boots up, the select input (R799) of the analog switch is asserted high
allowing for the processor to receive an accurate 32.768 kHz, 2.9 V peak-to-peak square wave. This
signal is generated by tapping the output of the 32.768 crystal and buffering the signal with the
following components: U713, R745, R746, C743, C792, R742, and R741. The 32.768 kHz clock
signal allows for the completion of real-time applications.

4.4.6.3.2 ESD Protection Circuitry

Several components on the VOCON section were added to protect the circuitry from Electrostatic
Discharge (ESD). The side connector signal lines are exposed and require ESD protection
components. These protection components include:
• 5.6 volt zeners (VR659 and VR662) on the CTS and RTS lines, microphone lines, and the
option select lines
• 12 volt zener (VR650) on the internal and external speaker audio lines
• 13 volt zener (VR658) on the OPTB+ line, and
• low capacitance ESD suppressors (VR678, VR651, and VR652) on the USB data lines.

4.4.6.3.3 Universal Connector (Side Connector) Interface Circuitry

An important circuit in the side connector interface is the Option Select 2 line comparator. The
op-amp (U601) is used as a comparator for the option select 2 line. The voltage divider network of
R658 and R673 determines the comparator threshold. The remaining components on the side
connector interface consist of current-limiting serial resistors and noise-suppressing shunt
capacitors.
4.4.6.3.3.1 Universal Connector (Side Connector) and Option Selects
The universal connector is located on the side of the radio. It is the external port or interface to the
outside, and is used for programming and interfacing to external accessories. The universal
connector is connected to the main board via a flex circuit at connector J650.
6816985H01-F
4.4-13
February 14, 2012