Gymna Pulson 330, Руководство по обслуживанию

Страница: 13 / 49

10. Microcontroller circuits.
10.1 The microprocessor (
µ
p).
The pulson 330 uses a Z86E21, a One Time Programmable (OTP)
microcontroller which controls all sequences necessary for the
apparatus to function.
It has on board ROM (8K), and RAM. Clock speed is defined by an
external crystal, which runs at 12 MHz.
10.2 Microprocessor guard components.
To monitor the proper functioning of the
µ
p, some external components
are added.
1. U2 (MAX1232):
µ
p supervisor IC.
Does constant monitoring of VCC. When it goes below 4.75 V, a
pulse with a fixed length is produced, to assure a good reset
of the
µ
p.
R7 is a pull-up resistance and C3 filters out burst signals
which may possibly disturb the
µ
p.
U2 also monitors the watchdog output of the
µ
p. In case of
processor hang-up,
the same reset pulse is given.
2. U6 (74HC4538): output circuit protection IC.
In case of processor hang-up, the output stage has to be
switched off
immediately.
When the output VUS_EN goes low/high, Q10 switches and AMP_US
goes to
zero. This IC is also controlled by the watchdog output of the
µ
p.
10.3 I ≤ C bus
The combination of outputs SCK and SCD forms a serial bus which
follows the I•C protocol.
A maximum of 10 components, each having their own address, can be
connected.
In this case 3 components are connected.
1. U10 (24C16)
This is a 2K eeprom, which can be written during the special
service routine.
It contains the calibration data of the output stage and a
copy of the checksum from the
µ
p ROM. Each time the instrument
is switched on, the
µ
p calculates
the ROM checksum and compares it to the value in the eeprom.
In case of difference an error code will be displayed. Refer
to error codes:
2. U15 (PCF8591)
ADDA IC. Data coming from and going to this IC are sent by the
I•C bus.
For more information refer to US power circuits, page
3. Display.
Connection to the display pcb is made by CON7.
All display data arrive via this bus.
Page 13