Intel MCS 51 User Manual page 280

intd.
83C152 HARDWARE DESCRIPTION
PIN DESCRIPTION
(Continued)
Pin #
DIP
9
37
39
23
22
N/A
NIA
N/A
PLCC(l)
13
55
54
56
32
31
17,20
21,22
38,39
40,49
67,66
52,57
50,66
1,51
12
53
Description
=-Reset input.A logiclowon this pinfor three machinecycleswhilethe
oscillatoris runningresetsthe device.An internalpullupresistorpermitsa power-
on reset to be generatedusingonlyan externalcapacitorto V.SS. A lthoughthe GSC
recognizesthe reset after three machinecycles,data may continueto be
transmittedfor UPto
4
machinecyclesafter Reset is firstapplied.
ALE—Addresa Latch
Enable output
signal forlatching t helowbyteoftheaddress
during accesses t oexternal
m emory.
In normaloperationALE is emitted at a constantrate of 1/6the oscillatorfrequency,
and may be usedfor externaltimingor clockingpurposes.Note, however,that one
ALE pulseis skippadduringeach access to externalData Memory.Whilein Reset
ALE remainsat a constanthighlevel.
PSEN-Program Store Enable isthe Read strobeto ExternalPro ram Memory.
-+ When the 8XC152 is executingfrom externalprogrammemory,P EN isactive
(low).When the device is executingcode fromExternalProgramMemory,= is
activatedtwiceeach machinecycle, exceptthat two= activationsare skipped
duringeach accessto ExternalData Memory.While in Reset = remainsat a
constanthiahlevel.
~-External Accessenable. = mustbe externallypulledlowin orderto enable
the 8XC152 to fetch code from ExternalProgramMemory
locations O OOOH to
OFFFH.
~ mustbe connectedto VCCfor internalprogramexecution.
XTAL1-lnputto the invertingoscillatoramplifierand inputto the internalclock
generatingcircuits.
XTAL2-Output f romtheoscillator amplifier.
Port S-Port 5 is an 8-bit bi-directional 1 /0 portwithinternalpullups.Port5 pins
that have 1s writtento them are pulledhighbythe internalPUIIUPS, and inthat state
can be usedas inputs.As inputa,Port5 pinsthat are externallybeingpulledlowwill
sourcecurrent(IIL,on the data sheet) becauseof the internalpullups.
Port5 is also the multiplexedIow-orderaddreasand data busduringaccessesto
externalprogrammemoryif EBEN is pulledhigh.In this applicationit usesstrong
OUIIUOS whenemittina1s.
Port 8-Port 6 isan 6-bit bi-directional 1 /0 portwithinternalpullups.Port6 pins
that have Is writtento them are pulledhigh
bytheinternal pulluPs, andinthatstate
can be usedas inputa.As inputs,Port6 pinsthat are externallypulledlowwill
sourcecurrent(lIL,on the data sheet) becauseof.the internalPUIIUPS.
Port6 emitsthe high-orderaddress byteduringfetches from externalProgram
Memory
if
EBEN is pulledhigh.In thisapplicationit uses strongpullupswhen
emitting1s.
EBEN-E-Bus Enableinputthat designateswhetherprogrammemoryfetchestake
place via Ports O and 2 or Ports 5 and 6. Table 2.1 shows how the ports are
used in
conjunction with
EBEN.
EPSEN-E-bus ProgramStore Enable isthe Read strobeto externalprogram
memorywhen EBEN is high.Table 2.1 showswhen= is usedrelativeto
~ depending
on thestatus of
EBEN
and=.
1. N.C.Dinson PLCC Paclws mavbe connectedto internal d ie snd ehouldnotbe used
in customer applications.
2. It is kcommended~hatk-th Pi; 3 and Pin 33 be grounded forPLCC devices.
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