Microprocessor Architecture
Intel 8085 Pin Configuration
The 8085 Buses
Intel 8085 Pin Configuration
The 8085 Buses
n The
8085 is an 8-bit general purpose
microprocessor that can address 64K Byte of memory.
n It
has 40 pins
and uses +5V for power. It can run at a maximum frequency of 3 MHz.
nThe
pins on the chip can be grouped into 6 groups:
n Address Bus.
n Data Bus.
n Control and Status
Signals.
n Power supply
and frequency.
n Externally Initiated Signals.
n Serial I/O ports.
The
Address and Data Bus Systems
n The
address bus has 8 signal lines A8 – A15
which are unidirectional.
nThe
other 8 address bits are multiplexed
(time shared) with the 8 data bits.
n So,
the bits AD0 – AD7 are bi-directional
and serve as A0 – A7 and D0
– D7
at the same time.
n During
the execution of the instruction, these lines carry the address bits during the
early part, then during the late parts of the execution, they carry the 8 data
bits.
n In
order to separate the address from the data, we can use a latch to save the
value before the function of the bits changes.
The
Control and Status Signals
n There
are 4
main control
and status
signals.
These are:
nALE:
Address Latch Enable.
This signal is a pulse that become 1 when the AD0 – AD7
lines have an address
on them.
It becomes 0 after that. This signal can be used to enable a latch to
save the address bits from the AD lines.
nRD:
Read. Active low.
nWR:
Write. Active low.
nIO/M:
This signal specifies whether the operation is a memory
operation
(IO/M=0) or an I/O
operation
(IO/M=1).
nS1 and S0 : Status signals to specify the kind of operation being performed. Usually not used in
small systems.
