Intel MCS 51 User Manual

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 thispinforthreemachinecycleswhilethe
oscillatorisrunningresetsthe device.An internalpullupresistorpermitsa power-
on resetto be generatedusingonlyan externalcapacitorto V.SS.Althoughthe GSC
recognizesthe resetafterthree machinecycles,data may continueto be
transmittedforUPto
4 machinecyclesafterResetisfirstapplied.
ALE—AddresaLatchEnableoutputsignalforlatchingthelowbyteoftheaddress
duringaccessestoexternal
memory.
In normaloperationALEisemittedat a constantrateof 1/6the oscillatorfrequency,
and maybe usedforexternaltimingor clockingpurposes.Note, however,thatone
ALEpulseisskippadduringeach accessto externalData Memory.Whilein Reset
ALEremainsat a constanthighlevel.
PSEN-Program Store Enableisthe Read strobeto ExternalPro ramMemory.
-+Whenthe 8XC152 isexecutingfromexternalprogrammemory,P EN isactive
(low).When the deviceisexecutingcodefromExternalProgramMemory,= is
activatedtwiceeach machinecycle,exceptthattwo= activationsare skipped
duringeach accessto ExternalData Memory.Whilein Reset = remainsat a
constanthiahlevel.
~-External Accessenable.= mustbe externallypulledlowin orderto enable
the8XC152 tofetchcodefrom ExternalProgramMemory
locationsOOOOHto
OFFFH.
~ mustbe connectedto VCCforinternalprogramexecution.
XTAL1-lnputto the invertingoscillatoramplifierand inputto the internalclock
generatingcircuits.
XTAL2-Outputfromtheoscillatoramplifier.
Port S-Port 5 isan 8-bitbi-directional1/0 portwithinternalpullups.Port5 pins
that have 1swrittento them are pulledhighbythe internalPUIIUPS,andinthat state
can be usedas inputs.As inputa,Port5 pinsthatare externallybeingpulledlowwill
sourcecurrent(IIL,onthe datasheet) becauseof the internalpullups.
Port5 isalsothe multiplexedIow-orderaddreasanddata busduringaccessesto
externalprogrammemoryifEBEN ispulledhigh.Inthisapplicationitusesstrong
OUIIUOSwhenemittina1s.
Port 8-Port 6 isan 6-bitbi-directional1/0 portwithinternalpullups.Port6 pins
that have Is writtento them are pulledhigh
bytheinternalpulluPs,andinthatstate
can be usedas inputa.As inputs,Port6 pinsthatare externallypulledlowwill
sourcecurrent(lIL,onthe data sheet) becauseof.theinternalPUIIUPS.
Port6 emitsthe high-orderaddressbyteduringfetchesfromexternalProgram
Memory
ifEBENispulledhigh.In thisapplicationituses 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
conjunctionwith
EBEN.
EPSEN-E-bus ProgramStoreEnableisthe Read strobeto externalprogram
memorywhenEBENishigh.Table 2.1 showswhen= isusedrelativeto
~ depending
on thestatusofEBENand=.
1.N.C.DinsonPLCCPaclws mavbeconnectedto internaldiesndehouldnotbe used
in customer applications.
2.Itiskcommended~hatk-th Pi; 3 andPin33be groundedforPLCCdevices.
7-16

Intel MCS 51 Specifications

General

Brand	Intel
Model	MCS 51
Category	Microcontrollers
Language	English