Intel MCS 51 User Manual

i~.
83C152 HARDWARE DESCRIPTION
I
P2 PCH
x
SARH.
x
PCH
“~
~OUACYCLE~REs#c&yM
27@427-31
Figure 4.4. DMA Transfer from External Memory to Internal Memory
~’z Os’”p~R’”o’~’2 Os’‘“’””~
ALE
I
I
I
F2m
PO ~-~~~- - ‘ -- ;Lii-- ‘B;i;ir
OARLn
x
OATAOUT
. . ------------
----
x
X’4::E
‘2 PCH
x
SARHn
x
OARH.
x
Pm
I
270427-S2
Figure 4.5. DMATranafer from External Memory to External Memory
4.3.1
REQUESTERMODE
4.3.2ARBITERMODE
The RequesterMode is selectedby settingthe control
For DMAsthat are to be drivenby somedeviceother
bit lU3Q,whichresidesin PCON. In that mode,when
than the C152,a different versionof the Hold/Hold
the C152wantato doa DMAto ExternalData Merno-
Acknowledgeprotocolis available.In this veraiosz,the
ry, it first generatesa Hold Requestsignal,~, and
devieewhichis to drive the DMA sendsa Hold R+
waits for a Hold Acknowledgesignal,HLDA, before
questsignal,~, to the
C152.If the C152is current-
commencingthe DMA o lyperforminga DMAto or fromExternalData Memo-
execution continues while HLDA is awaited. The
DMA is not begununtil a logicalOis detected at the
I’Y,it willcompletethis DMAbeforerespondingto the
Hold Request.When the C152respondsto the Hold
HLDA pin. Then,oncethe DMA hasbegun,it goesto Request,it doesso by activatinga HoldAcknowledge
completionregardlessof the logiclevelat HLDA.
sigd, HLDA. This indicates that the C152will not
commencea new DMA to or from External Data
The protoed is aetivatex-1onlyfor DMAs(not for pro-
Memorywhile~ remains active.
P fetches or MOVX operations), and only for
DMAs to or thn External Data Memory.If the data Note that in the Arbiter Modethe C152doesnot sus-
destination and sourceare both internal to the C152,
penalprogramexecutionat all, evenif it is executing
the ~/RR protocolis not used. from externalprogrammemory.It doesnot surrender
w of its ownbus.
The HLD output is an alternate functionof port pin
P1.5, and the HLDA input is an alternate firnctionof The Hold Requestinput, ~, is at P1.5.The Hold
port pin P1.6.
Acknowledge output,
HLDA, is at P1.6. This
7-51

Intel MCS 51 Specifications

General

Brand	Intel
Model	MCS 51
Category	Microcontrollers
Language	English