7480 datasheet(254/337 Pages) RENESAS

254 / 337 page

7480 Group and 7481 Group User's Manual

2-39

2.8 Countermeasures against Noise

APPLICATIONS

Noise

XIN

XOUT

VSS

XIN

XOUT

VSS

N.G.

O.K.

7480 Group

7481 Group

7480 Group

7481 Group

Figure 2.8.2 Wiring for Clock I/O Pins

P33/VPP

Approximately

Ω

7480 Group

7481 Group

Figure 2.8.3 Wiring for VPP Pin of One Time PROM

and EPROM Version

(2)

Wiring for Clock I/O Pins

• Make the length of wiring which is connected

to clock I/O pins as short as possible.

• Make the length of wiring (within 20 mm)

across the grounding lead of a capacitor

which is connected to an oscillator and the

VSS pin of a microcomputer as short as

possible.

• Separate the VSS pattern only for oscillation

from other VSS patterns.

REASON

A microcomputer’s operation synchronizes with

a clock generated by the oscillator (circuit). If

noise enters clock I/O pins, clock waveforms

may be deformed. This may cause a

malfunction or program runaway.

Also, if a potential difference is caused by the

noise between the VSS level of a microcomputer

and the VSS level of an oscillator, the correct

clock will not be input in the microcomputer.

(3)

Wiring for VPP Pin of One Time PROM

Version and EPROM Version

(In the 7480 Group and 7481 Group, the VPP

pin is also used as the P33 pin)

Connect an approximately 5 k

Ω resistor to

the VPP pin the shortest possible in series.

Note: Even when a circuit which included an

approximately 5 k

Ω resistor is used in

the

Mask

ROM

version,

the

microcomputer operates correctly.

REASON

The VPP pin of the One Time PROM and the

EPROM version is the power source input pin

for the built-in PROM. When programming in

the built-in PROM, the impedance of the VPP

pin is low to allow the electric current for writing

flow into the PROM. Because of this, noise

can enter easily. If noise enters the VPP pin,

abnormal instruction codes or data are read

from the built-in PROM, which may cause a

program runaway.

7480 Datasheet(PDF) 254 Page - Renesas Technology Corp

7480 Datasheet(HTML) 254 Page - Renesas Technology Corp

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL