5

Input Port Mode 0 - Typical Operation

General Operation

becomes an input port. In this mode, the peripheral device

places data into the CDP1852 with a strobe pulse and the

CDP1852 signals the microprocessor that data is ready to be

transferred on the strobe’s trailing edge via the SR output

line. The CDP1802 then issues an input instruction that

enables the CDP1852 to place the information from the

peripheral device on the data bus to be entered into a mem-

ory location and the accumulator of the microprocessor.

Detailed Operation (See Figure 5)

The STROBE from the peripheral device places DATA into

the 8-bit register of the CDP1852 when it goes high and

latches the DATA on its trailing edge. The SR output is set

low on the strobe’s trailing edge. This output is connected to

a flag line of the CDP1802 microprocessor and software poll-

ing will determine that the flag line has gone low and periph-

eral data is ready to be transferred. The CDP1802 then

the MRD line also high, the CDP1852 is selected and its out-

put drivers place the DATA from the peripheral device on the

DATA BUS. When the CDP1802 selected the CDP1852, it

also selected and addressed the memory via one of the 16

internal address registers selected by an internal “X” regis-

ter. The data from the CDP1852 is therefore entered into the

memory [Bus

→ M(R(X))]. The data is also transferred to the

D register (accumulator) in the microprocessor (Bus

→ D).

When the CDP1802’s execute cycle is completed, the

data output pins are three-stated. The SR output returns

high.

Minimum Data Setup Time

5-

-10

0

ns

10

-

-5

0

ns

Minimum Data Hold Time

5

-

75

150

ns

10

-

35

75

ns

Data Out Hold Time (Note 2)

5

30

185

370

ns

10

15

100

200

ns

Select to Data Out (Note 2)

5

30

185

370

ns

10

15

100

200

ns

Clear to SR

5

-

170

340

ns

10

-

85

170

ns

Clock to SR

5

-

110

220

ns

10

-

55

110

ns

Select to SR

5

-

120

240

ns

10

-

60

120

ns

NOTES:

2. Minimum value is measured from CS2, maximum value is measured from CS1/CS1.

Dynamic Electrical Specifications

and 1 TTL Load (Continued)

PARAMETER

(V)

LIMITS

UNITS

MIN

(NOTE 1)

TYP

MAX

CDP1852, CDP1852C