Teledyne 4700, Serivce Manual

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4700 Refrigerated Sampler Service Guide
Section 4 CPU and Power Supply
4-2
The processor has a 16-bit data bus so that two bytes at a time
are handled between the CPU and memory. Eight bits of the data
bus also go to the LCD display. The logic for address decoding is
built into the CPU, so there is no external logic to generate the
chip selects to the memories and display.
Three temperatures, 2 voltages, and an analog signal from the
liquid detector go into the a-to-d inputs. Likewise, the serial
signals to/from the internal UART go to an RS-232 d-to-a con-
verter chip. Approximately 28 digital I/O lines come directly from
the CPU. Additional I/O lines are provided by the I/O expanders.
These chips communicate with the CPU over an SPI bus (serial
peripheral interface). The lines SPCK, MOSI, and MISO provide
the data path for this communication.
The CPU contains an internal watchdog circuit, but this is not
being used.
The CPU has built-in RAM for some special functions, such as
reprogramming the FLASH, but is not used for normal oper-
ation, such as storing variables.
4.1.2 Memory – U26, 27 U26 is the flash memory that contains the boot code and appli-
cation code, and the text strings for all languages that may be
available. It has a capacity of 4 Mb. At present, the application
code is about 180 K, which is less than 5% of the total flash.
U27 is the RAM memory. It is static RAM and contains 512 K
bytes. It is backed up by an on-board lithium battery.
4.1.3 I/O Ports – U11, 14 These are I/O expander chips that communicate serially with the
CPU over the SPI bus. U14 provides 6 outputs that are column
drivers for the keypad, which is arranged in a 4-by-6 matrix. The
4 row signals come back directly to the CPU. The keypad is not
continuously scanned. Normally the column lines are pulled low
by the port and the row lines are pulled high by pull-up resistors.
If a switch is pushed, one of the row lines goes low. The 4 row
inputs are programmed in the CPU to generate an interrupt that
then scans the columns by taking them low one at a time.
U11 provides outputs for the distributor motor and refrigeration
controls.
4.1.4 Power Supplies – U12,
13, 15, VR1, P11
Twelve-volt power comes into the board on P11. The current goes
through PTC R34 and then to protection in the form of a tran-
szorb and capacitors. The 12 volts goes through a voltage divider
(R97-98) to an a-to-d input so the diagnostics can monitor the
input voltage. The 12 volts is split into 3 paths with various
degrees of filtering. The lightly fi12V goes to the pump
drive circuitry, beeper, and case heater. +VIN goes to the 5-volt
switching regulator. Vp, with the most filtering, goes to the 3.3V
regulator and the 5V linear regulator.
U13 is a switching regulator that operates from Vp. The 3.3 volts
from this regulator supplies the CPU, memory, and most of the
other ICs. 3.3 volts also goes through an LC filter (L7-C44) to
power the analog 3.3V circuits.