ITCI Brasov CoBra, Описание аппаратуры, Страница: 5 / 63

— RS-232 interface for use with a printer or another computer.
— external memory (magnetic tape) interface.
— audio interface.
— keyboard interface (6x8 key matrix).
— 8 bit input port for general use or used as a
Kempston -compatible
joystick interface.
The conventional keyboard is built on a separate board, as an extended
6x8 key matrix plus ZX S compatible compound keys.
The floppy disk interface is built on a third board around the i8272A
Floppy Disk Controller circuit assisted by the Z80-CTC counter/timer circuit.
1.2 CENTRAL PROCESSING UNIT
The central processing unit is built with the 8-bit microprocessor Z80A .
Z80A is a MOS-LSI integrated circuit in a 40-pin DIP package, having 3 buses:
— the data bus;
— the address bus;
— the control bus.
The data bus
D0 — D7 is a three-state input/output bus, used for
exchanging information with the memory and the I/O interface circuits.
Z80A falls within the 8-bit microprocessor category, having the capability
to process 8 bits of information simultaneously on its data bus.
The 16-bit address bus is used to address the memory or the I/O devices
during the information exchanges.
Having 16 bits for the address bus, Z80A can address 64 KB of memory
and an additional 64 KB space dedicated to the I/O devices.
The control bus offers the signals required for monitoring the data
transfer to/from microprocessor.
The microprocessor can perform different tasks:
— reads data from memory;
— writes data to memory;
— reads data from I/O devices;
— writes data to I/O devices;
— performs arithmetic operations on data.
Z80A executes a range of 158 types of instructions. In the CoBra
microcomputer, the microprocessor clock signal has a 3.5 MHz frequency.
Pin description:
A0-A15 — the address bus;
— three-state logic outputs, active in “1” logic level;
— can address up to 64 KB memory and I/O devices;
— in the case of I/O, the 8 less significant address bits are used to
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