7-12
Theory of Operation
On the K1
µ
P the lines XIRQ (U0101-30), MODA LIR (U0101-77), MODB
VSTPY (U0101-76) and RESET (U0101-75) should be logic high during all
normal K1
µ
P operation. Whenever a data or an address line becomes unloaded or
shorted to an adjacent line, a common symptom is that short negative pulses occur
on the RESET line, with a period of 20 msec. When two lines are short-circuited,
mid logic level (around 2.5 V) may be observed, while these lines are opposite
driven by two different ICs.
The MODA LIR (U0101-77) and MODB VSTPY (U0101-76) inputs to the K1
µ
P
must be at a logic 1 level for proper operation. After the K1
µ
P starts execution, it
will periodically pulse these lines to determine the desired operating mode. While
the Central Processing Unit (CPU) is running a new instruction, MODA LIR (as
an open-drain CMOS output) drops low.
However, since it is an open-drain output, the signal waveform rise has an
exponential shape, like an RC circuit.
The
µ
P has eight analog-to-digital converter ports (A/D): PE0 to PE7. These lines
may measure voltage levels in the range of 0 to 5 V and convert that level to a
number ranging from 0 to 255 which can be read by the software to take
appropriate action.
For example, U0101-46 is the battery voltage detect line. R0641 and R0642 form
a resistor divider on SWB+. With 30K and 10K and a voltage range of 11 V to 17
V, that A/D port would see 2.74 V to 4.24 V which would then be converted to
digital values of ~140 to 217 respectively.
U0101-51 is the high reference voltage for the A/D ports on the K1
µ
P. Resistor
R0106 and capacitor C0106 filter the +5 V reference. If this voltage is lower than
+5 V the A/D readings will be incorrect. Likewise U0101-50 is the low reference
for the A/D ports. This line is normally tied to ground. If this line is not connected
to ground, the A/D readings will be incorrect.
Capacitors C0104, C0105 serve to filter out any AC noise which may ride on +5V
at U0101.
Input IRQ (U101-61) generates an interrupt, if either HOOK (J0101-3) is higher
than 6V (SBEP communication) or a low at the option interrupt pin (J0103-8)
turns Q0124 off and Q0125 on. The K1
µ
P determines the interrupt source by
reading the collector of Q0104 via U0101-6 and the collector Q0124 via U0101-7.
One-Time Programmable
(OTP) Memory
The 128-KByte OTP memory (U0102) contains the radio’s operating software.
This memory is read-only. The memory access signals (CE, OE and WE) are
generated by the
µ
P.
The OTP memory is factory-programmed once only.
Capacitor C0131 serves to filter out any AC noise which may ride on +5V at
U0101, and C0132 filters out any AC noise on Vpp.
Electrically Erasable
Programmable Memory
(EEPROM)
EEPROM (U0104) contains the radio’s operating parameters such as operating
frequency and signalling features, commonly known as the codeplug. It is also
used to store radio operating state parameters such as current mode and volume.
U0104 is a 4 Kbyte device. This memory can be written to in excess of 100,000
times and will retain the data when power is removed from the radio. The memory
