Icom IC-M88 CPU–Continued, 4-5-2EXPANDER IC (MAIN UNIT; IC341), 4-5-3D/A CONVERTOR IC (MAIN UNIT; IC251)

CPU–Continued

Pin	Port		Description
number	name
111	DOWN	Input port for the [DOWN] key.
		Low	: While [DOWN] key is pushed.
112	CH/WX	Input port for the [CH/WX] key.
		Low	: While [CH/WX] key is pushed.
113	16/9	Input port for the [16/9] key.
		Low	: While [16/9] key is pushed.
114	SCAN	Input port for the [SCAN] key.
		Low	: While [SCAN] key is pushed.
115	H/L	Input port for the [H/L] key.
		Low	: While [H/L] key is pushed.
119	UNLK	Input port for the PLL unlock signal.
		High : PLL lock voltage is unlocked.

4-5-2 EXPANDER IC (MAIN UNIT; IC341)

Pin	Port	Description
number	name
		Outputs the AF mute switch (IC281,
5	SRXMS	pin 3) control signal.
		Low : While the scrambler decording
		signal is muted.
		Outputs the AF mute swtich (IC281,
6	DETMS	pin 7) control signal.signal.
		Low : While AF signal is muted.
		Outputs the scrambler IC’s clock shift
7	CKSIS	control signal.
		High : While the clock is shifted.
		Outputs the RF attenuator control
11	ATTS	signal.
		High : While attenuator is ON.
		Outputs the TX mute swtich (Q141)
12	TXMS	control signal.
		Low : While receiving.
13	VCOS	Outputs the TX/RX VCO control
		signal.

4-5-3 D/A CONVERTOR IC (MAIN UNIT; IC251)

Pin	Port	Description
number	name
2	SQCON	Outputs squelch level control signal.
3	MOCON	Outputs modulatin level control signal.
10	DTCON	Outputs DTCS modulation balance
		control signal.
11	FRCON	Outputs reference	frequency	level
		control signal.
14	T1CON	Outputs bandpass	filter1 tuned	and
		transmitting power control signals.
15	T2CON	Outputs bandpass filter2 tuned signal.
22	T3CON	Outputs bandpass filter3 tuned signal.
23	T4CON	Outputs bandpass filter4 tuned signal.

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