Cpu Board Circuit Description (Programmable Versions Only) - TTI TSX Series Service Manual

Overview
The power supplies use a Z80 microprocessor to accept and process commands (from the
keyboard, RS232 interface or GPIB interface) and to pass on the necessary command and
control information to a microcontroller, located on the other side of an opto-isolated interface,
which controls the setting of the values for voltage, current and OVP and the measurement of
output voltage and current. The opto isolated interface is later referred to as the Inter-
Processor-Interface or IPI.
The CPU board contains the Z80 microprocessor, program memory, data memory, RS232
interface, GPIB interface, keyboard scan circuitry and the interface to communicate with the
microcontroller. The microcontroller is also on the CPU board together with its display control
latches and drivers and the analog to digital converter which measures the output voltage and
current. The Z80 and microcontroller are electrically isolated from each other by an opto-coupled
interface. This allows the Z80 and its interfaces to operate at mains ground potential while the
microcontroller and the output of the power supply may be up to 300 Volts away from ground. The
circuitry on each side of the isolation interface is described below.
The Z80 uses a 4 digit LED display and 16 LEDS to communicate status information to the user,
The microcontroller uses two 4 digit LED displays to show voltage and current values at the
output. All LED displays are mounted on the keyboard pcb, see next section.
Z80 Circuit
The 4.9152MHz clock for the Z80 is generated by IC13 which also provides the 1.6ms clock used
as the NMI signal, the various clocks used to specify the RS232 interface baud rate and the
600Hz buzzer drive. The 1.6ms clock is used by the CPU as follows. Six ticks are used to
generate the LED display and the 16 status LEDs. The seventh tick is used to read the
continuously rotating pot and alternately to scan the keyboard and to generate timing delays for
the slower parts of the system or to update the system status.
The memory map is divided into a 56k byte area at IC10, which contains the system code in
ROM, and an 8k byte area at IC11 containing RAM which is battery backed and holds all the
system parameters and power supply stores. IC10 is mapped in the address range 0000H to
DFFFH (56k bytes) and IC11 is mapped in the address range E000H to FFFFH.
The input/output devices are selected by IC14 during IORQ cycles. Each output from IC14
selects a range of 8 ports as follows
00H to 07H
08H to 0FH
10H to 17H
18H to 1FH
20H to 27H
28H to 2FH
When the power fail line (PF bar on PJ1 pin 5) goes low the system immediately enters a reset
condition by Q6 turning on and discharging C2. This causes the reset lines, MRST and MRST
bar, to assume their active states and all circuitry is held in the reset condition. The ram, IC11 is
switched to battery power and disabled by pulling the chip select input high via the RAMSAVE
line thus ensuring that the contents are retained until power is restored.
CPU Board Circuit Description
(Programmable versions only)
RS232 serial device IC5.
7210 GPIB controller IC3.
Segment latch. Drives the LED display segment lines and scans the keyboard
rows.
Digit latch. Drives the LED display digit lines. Also controls the buzzer and NMI
enable signals.
Status read. Reads from keyboard columns, the pot adc and the IPI.
Control port. Writes to the IPI, sets the baud rate and controls the pot adc.
13