Monday, April 16, 2012
Status code for Intel 8085
RD (OUTPUT): It is a control signal sent by the microprocessor
to control read operation. The selected memory or I/O device is read when RD is
low.
WR (OUTPUT): It is a control signal issued by the microprocessor
to control write operation. The data on the data bus are written into the selected
memory or I/O device when WR is low.
HOLD (INPUT): When an external device wants to use address
and data bus it sends HOLD signal to the microprocessor. When microprocessor
receives HOLD signal it completes its current instruction at hand, and then
relinquishes control of b-uses to allow external device to use them.
HLDA (OUTPUT): It is a HOLD acknowledgement signal. It
is sent by the microprocessor to the external device to indicate that the HOLD
request has been received. On the completion of data transfer, the external
device removes the HOLD request. The HLDA goes low after the removal of HOLD
request.
INTR (INPUT): It is an interrupt signal of the lowest
priority.
INTA (OUTPUT): It is an interrupt acknowledgement
signal. It is issued by the microprocessor after INTR is received.
RST 5.5, 6.5, 7.5, TRAP (INPUT): These are
interrupts. The TRAP is nonmaskable and has the highest priority. Others are
maskable interrupts. The order of priority is TRAP, RST 7.5, RST 6.5, and RST
5.5.
RESET IN (INPUT): When this signal is applied the CPU is
brought to the reset condition. The contents of the program counter become
zero.
RESET OUT (OUTPUT): This signal indicates that the CPU is
being reset.
READY (INPUT): It is an input signal to the
microprocessor. It is sent by a peripheral to indicate whether it is ready to
tran-sfer data or not. The microprocessor examines READY signal before data are
transferred. If READY is high it shows that peripherals are ready to transfer
data. If READY is low the microprocessor waits till READY becomes high. The
status of READY is examined in the second clock cycle of a machine cycle.
X1 and X2 (INPUT): An external crystal oscillator is
connected through these terminals to supply clock for the microprocess-or. A
crystal oscillator drives an internal circuitry which is within the
microprocessor to produce suitable clock for the operation of the
microprocessor.
CLK (OUTPUT): The clock is also required by some
other ICs
Of the computer, Hence CLK is a clock
output from the micro-processor, which can be utilized for the operation of
other ICs.
SID (INPUT): It is an input line for serial data. The data rece-ived from this are loaded into
the 7th bit of the accumulator when RIM instruction is executed.
SOD (OUTPUT): It is an output line for serial data.
The 7th bit of the accumulator is sent through this line when SIM instruction
is executed.
