Intel MCS 51 User Manual page 312

1
83C152 HARDWARE DESCRIPTION
DMACHANNEL O
I
DMACHANNEL 1
,-
m, ~,- m,
DESTINATIONAODRESS I DESTINATIONADDRESS
m m : ,- m,
~ ,
SOURCEADDRSSS
I
SOURCEADORESS
,- m, ; ,- m,
BYTE COUNT
I
BYTECOUNT
m;
m
OMAO CONTROL
I
DMA1 CONTROL
+
t
Two new bits in PCON control
Hold/Hold Acknowkdge Iogk
270427-28
-. . . . . . . . . .
ueriods) oerbvte transferred. exeeotwhen thedestina-
kon and"sourk are both in'Exte&al Data RAM. In
that case the transfer takes two machine cycles per
byte. The term DMA Cycle will be used to mean the
transfer of a single&ta bytej whether it takeB1 or 2
machine cycles.
Associatedwitheach channel are sevenSFRS,shownin
Figure4.1.SARLnand SARI% holdsthe lowand high
bytes of the sourceaddress. Taken together they forma
id-bit SourceAddress Register. DARLn and DARHII
hold the lowand high bytea of the destinationaddress,
and together form the Destination Address Register.
BCRLnand BCRHnhold the lowand highbytesof the
number of bytes to be transferred, and together form
the Byte CountRegister.DCONn conteinscontroland
flag bits.
Two bits in DCONn are used to speeify the physical
destination of the data transfer. These bits are DAS
(DestinationAddressSpace)and IDA (IncrementDes-
tination Address). If DAS = O, the destination is in
data memoryexternal to the C152. If DAS = 1, the
destination is intemsl to the C152. If DAS = 1 and
IDA = O,the internal destinationis a SpecialFunction
Register (SFR).If DAS = 1 and IDA = 1,the inter-
nal destinationis in the 256-bytedata RAM.
In any case, if IDA = 1, the destination address is
automaticallyincremented after each byte transfer. If
IDA = O,it is not.
Two other bits in DCONn specifythe phyaiealsource
of the &ta to be transferred. These are SAS (Source
Address Space)and ISA (Increment Source Address).
If SAS = O,the source is in &ta memoryexternal to
the C152.IfSAS = 1,the aoureeis internal. If SAS =
1 and ISA = O,the internal source is an SFR. If SAS
= 1and ISA = 1,theioternsl sourceis in the 256-byte
data RAM.
In any case,ifLSA = 1,the sourceaddressis automati-
cally incrementedafter each byte transfer. If ISA = O,
it is not.
The functionsof thesefour ccmtrolbits are summarized
below:
DAS IDA
Destination Auto-lncrament
o 0
ExternalRAM no
o 1
ExternalRAM yes
1 0 SFR no
1 1 InternalRAM
yes
SAS ISA Source Auto-Increment
o
0 ExternalRAM no
o 1
ExternalRAM yes
1 0
SFR no
1 1 InternalRAM
yes
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