4-7

Functional Description

The CDP1851 has four modes of operation: input, output,

bidirectional, and bit-programmable. Port A is programmable

in all modes; port B is programmable in all but the

bidirectional mode. A control byte must be loaded into the

control register to program the ports. In the input and output

modes, each port has two handshaking signals, STROBE

and RDY. In the bidirectional mode, port A has four

handshaking signals: A RDY and A STROBE for input, B

RDY and B STROBE for output. If port A is programmed in

the bidirectional mode, port B must be programmed in the

bit-programmable mode. Each terminal of port A or B may

be individually programmed for input or output in the bit-

programmable mode. Since handshaking is not used in this

mode, the RDY and STROBE lines may also be used for bit-

programming if port A is not in the bidirectional mode.

Input Mode

When a peripheral device has data to input, it sends a

STROBE pulse to the PlO. The leading edge of this pulse

clears the RDY line, inhibiting further transmission from the

peripheral. The trailing edge of the STROBE pulse latches the

data into the PlO buffer register and also activates the INT line

to signal the CPU to read this data. The lNT pin can be wired

to the INT pin of the CPU or the EF lines for polling. The CPU

PARAMETER

CONDITIONS

LIMITS

UNITS

(V)

(V)

(V)

CDP1851

CDP1851C

MIN

(NOTE1)

TYP

MAX

MIN

(NOTE1)

TYP

MAX

Quiescent Device Current

-

0, 5

5

-

0.01

50

-

0.02

200

µA

-

0, 10

10

-

1

200

-

-

-

µA

Output Low Drive

(Sink) Current

0.4

0, 5

5

1.6

3.2

-

1.6

3.2

-

mA

0.5

0, 10

10

2.6

5.2

-

-

-

-

mA

Output High Drive

(Source) Current

4.6

0, 5

5

-1.15

-2.3

-

-1.15

-2.3

-

mA

9.5

0, 10

10

-2.6

-5.2

-

-

-

-

mA

Output Voltage Low-Level

(Note 2)

-

0, 5

5

-

0

0.1

-

0

0.1

V

-

0, 10

10

-

0

0.1

-

-

-

V

Output Voltage High Level

(Note 2)

-

0, 5

5

4.9

5

-

4.9

5

-

V

-

0, 10

10

9.9

10

-

-

-

-

V

Input Low Voltage

0.5,

4.5

-

5

-

-

1.5

-

-

1.5

V

0.5,

9.5

-

10

-

-

3

---

V

Input High Voltage

0.5,

4.5

-

5

3.5

-

-

3.5

-

-

V

0.5,

9.5

-

10

7

--

---

V

Input Leakage Current

Any

Input

0, 5

5

-

-

±1-

-

±1

µA

0, 10

10

-

-

±2

---

µA

Three-State Output Leakage

Current

0, 5

0, 5

5

-

-

±1-

-

±1

µA

0, 10

0, 10

10

-

-

±1

---

µA

Operating Current (Note 3)

-

0, 5

5

-

1.5

3

-

1.5

3

mA

-

0, 10

10

-

6

12

-

-

-

mA

Input Capacitance

-

-

-

-

5

7.5

-

5

7.5

pF

Output Capacitance

-

-

-

-

10

15

-

10

15

pF

NOTES:

CDP1802A system operating at maximum speed of 3.2MHz).

CDP1851, CDP1851C