Pcb Difference; Watchdog Circuit; Figure 4-10 Watchdog Circuit - Hytera MD78X Service Manual

Baseband Section
4.6

PCB Difference

The UHF1 PCB has three versions: D, F and H.
The watchdog circuit (in the figure below) is added in version F.
C937
1000p
R923 0
3V3D
C978
0.1u
4.6.1

Watchdog circuit

The watchdog circuit is used to prevent the radio from damage due to OMAP malfunction. If the
program works properly, U302 feeds pulse signal (25ms) to the watchdog circuit through RST_CTRL.
Otherwise, this pulse signal will be terminated and delayed for more than 1.6s so that U906 generates
the reset signal to reset OMAP.
Compared with version D & F, the difference in version H lies with the audio amplifier, which applies
TDA7297SA instead of TDA7297D.
3V3D
U910
5
SENCE
3
4
CT
C941
0.15u
R920
U906
1
MR
2
VCC
3
GND
4
PFI
RESET IC

Figure 4-10 Watchdog circuit

D913
1 2
RSET
MR
MBRM120LT1G
D912
2
0
MBRM120LT1G
8
WDO
7
/RST
R983
6
WDI
5
PFO
18
Service Manual
R932
/PRST1
4.7K
1
1
0
/PRST
RST_CTRL