CDP1851 Просмотр технического описания (PDF) - Intersil
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CDP1851 Datasheet PDF : 14 Pages
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CDP1851, CDP1851C
then executes an input or a load instruction, depending on the
mapping technique used. In either case the proper code must
be asserted on the RAO, RA1, and CS lines to read the buffer
register (see Table 6).
The INT line is deactivated on the leading edge of TPB. The
trailing edge of TPB sets the RDY line to signal the periph-
eral that the port is ready to be loaded with new data. If RDY
is low when the input mode is entered (i.e. after a reset), a
“dummy” read must be done to set RDY high and signal the
peripheral device that the port is ready to be loaded.
Output Mode
A peripheral STROBE pulse sent to the PlO generates an
interrupt to signal the CPU that the peripheral device is
ready for data. The CPU executes the proper output or store
instruction. Data are then read from memory and placed on
the bus. The data are latched into the port buffer at the end
of the window when RE/WE = 0 and WR/RE = 1. The RDY
line is also set at this time, indicating to the peripheral that
there is data in the port buffer. The INT line is deactivated at
the beginning of the window. After the peripheral reads valid
port data, it can send another STROBE pulse, clearing the
RDY line and activating the INT line as in the input mode.
Bidirectional Mode
This mode programs port A to function as both an input and
output port. The bidirectional feature allows the peripheral to
control port direction by using both sets of handshake signals.
The port A handshaking pins are used to control input data
from peripheral to PlO, while the port B handshaking pins are
used to control output data from PlO to peripheral. Data are
transferred in the same manner as the input and output
modes. Since A INT is used for both input and output, the sta-
tus register must be read to determine what condition caused
A INT to be activated (see Table 5).
Bit-Programmable Mode
This mode allows individual bits of port A or port B to be
programmed as inputs or outputs. To output data to bits
programmed as outputs, the CPU loads a data byte into the
8-bit port as in the output mode (no handshaking). Only bits
programmed for outputs latch this data. Data must be stable
when reading from bits programmed as inputs, since the
input bits do not latch. When the CDP1851 inputs data to the
CPU the CPU also reads the output bits latched during the
last output cycle. The RDY and STROBE lines may be used
for I/O by using the STROBE/RDY I/O control byte in Table 2.
An additional feature available in the bit-programmable
mode is the ability to generate interrupts based on
input/output byte combinations. These interrupts can be
programmed to occur on logic conditions (AND, OR, NAND,
and NOR) generated by the eight I/O lines of each port (The
STROBE and RDY lines cannot generate interrupts).
TPB
MRD
MWR
TPA
A0
A1
CDP1800
FAMILY
µP
A2
A3
A4
A5
A6
A7
INT
BUS 0-7
VDD
10kΩ
TPB
WR/RE
RD/WE
CLOCK
RA0
RA1
PIO
NO. 1
CDP1851
CS
B INT
A INT
BUS 0-7
A RDY
B RDY
A STROBE
B STROBE
PORT A0 - A7
PORT B0 - B7
ADDRESS REGISTER
ADDRESS
SELECTS
8001 No. 1 Control/Status Reg
8002 No. 1 Port A
8003 No. 1 Port B
8004 No. 2 Control/Status Reg
8008 No. 2 Port A
800C No. 2 Port B
TPB
WR/RE
RD/WE
CLOCK
RA0
RA1
CS
A INT
B INT PIO
NO. 2
CDP1851
A RDY
B RDY
A STROBE
B STROBE
PORT A0 - A7
PORT B0 - B7
FIGURE 2. MEMORY SPACE I/O. THIS CONFIGURATION ALLOWS UP TO FOUR CDP1851s TO OCCUPY MEMORY SPACE 8XXX WITH
NO ADDITIONAL HARDWARE (A4-A5 AND A6-A7 ARE USED AS RA0 AND RA1 ON THE THIRD AND FOURTH PIO’s)
4-8
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