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Functional Description
The Cobra models MRF55 and MRF75 are Marine band FM Radio transceivers operated in the
frequency range 156.025MHz to 163.275MHz with WX and DSC. Functional as follows:
1. MRF55: Channel Up / Down, Emergency channel key CH16/9, WX/UIC key, Channel Scan key, TX
power HI/Low key, Dual watch channel key, Call/set key, Distress key, Squelch control volume, DC power
ON/Off and Audio Volume control, External Speaker Jack and GPS Jack, PTT key.
2. MRF75: Channel Up / Down, Emergency channel key CH16/9, WX/UIC key, MEMO Channel Scan key,
TX power HI/Low key, Tri watch channel key, Call/set key, Distress key, Squelch control volume, DC
power ON/Off and Audio Volume Up/Down control, PA Function, External Speaker & PA Jack and GPS
Jack, PTT key.
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MCU Description
The MCU uses Toshiba’s TMP86CM47U micro-controller, there are 32k X 8bits ROM and 1k X
8bits RAM, LQFP44 pins package. These pin assignment as below table:
PIN
Description
Model PIN
Description
Model
1
Vss = GND
55/75
23
Control LCD SDI data pin
55/75
2
X-in, crystal 8 MHz
55/75
24
WX alert data pin detect
55/75
3
X-out, crystal 8 MHz
55/75
25
TX Hi / low power control
55/75
4
Test, connect to GND.
55/75
26
Keys scan pin
55/75
5
Vdd, +5VDC input
55/75
27
Keys scan pin
55/75
6
DC power on control
F75
28
Beep tone Hi/low control
55/75
7
TX on/off control (on = low)
55/75
29
Digital volume data pin
F75
8
Reset pin
55/75
30
Digital volume clock pin
F75
9
DC power on key scan
F75
31
Open
55/75
10
LCD backlight control
55/75
32
EEprom clock pin
55/75
11
LCD backlight control
55/75
33
RX/TX signal indication
55/75
12
NMEA (GPS data) input
55/75
34
Pull high to +5VDC
55/75
13
EEprom data pin
55/75
35
AVDD (c5VDC)
55/75
14
Volume down key scan
F75
36
AVSS (connect to GND)
55/75
15
Volume up key scan
F75
37
16
Squelch output control
55/75
38
17
Inhibit audio when DSC on
55/75
39
18
Control LCD driver A0 data pin
55/75
40
19
PLL STB. HI=F75, Low=F55
55/75
41
Pin 37 to 41 for 1300Hz and
2100Hz FSK generator.
55/75
20
PLL clock data output
55/75
42
PLL data output
55/75
21
Beep tone generator
55/75
43
DSC detect pin
55/75
22
Control LCD CS1 pin
55/75
44
Squelch input detect
55/75
Remarks: MCU pin19 (BUS14) for MRF55 and MRF75 models select by resistor R371 and
R340 control. R371 open for MRF55 model, R340 open for MRF75 model selection.