參數(shù)資料
型號(hào)： DS80C323ENG
英文描述： Microprocessor
中文描述： 微處理器
文件頁(yè)數(shù)： 10/38頁(yè)
文件大?。?/td> 434K
代理商： DS80C323ENG
DS80C320/DS80C323
110196 10/38
TYPICAL MEMORY CONNECTION
Figure 3
DS80C320/
DS80C323
PORT 3
(8)
PORT 1
(8)
PSEN
ALE
OE
CE
CE
MSB ADDRESS
(3)
(7)
(8)
(8)
LSB ADDRESS
RD (P3.7)
WR (P3.6)
OE
WE
2K x 8
32K x 8
EPROM
LATCH
AD0–AD7
P2.0–P2.7
STRETCH MEMORY CYCLE
The DS80C320/DS80C323 allows the application soft-
ware to adjust the speed of data memory access. The
microcontroller is capable of performing the MOVX in as
little as two instruction cycles. However, this value can
be stretched as needed so that both fast memory and
slow memory or peripherals can be accessed with no
glue logic. Even in high–speed systems, it may not be
necessary or desirable to perform data memory access
at full speed. In addition, there are a variety of memory
mapped peripherals such as LCD displays or UARTs
that are not fast.
The Stretch MOVX is controlled by the Clock Control
Register at SFR location 8Eh as described below. This
allows the user to select a stretch value between zero
and seven. A Stretch of zero will result in a two machine
cycle MOVX. A Stretch of seven will result in a MOVX of
nine machine cycles. Software can dynamically change
this value depending on the particular memory or
peripheral.
On reset, the Stretch value will default to a one resulting
in a three cycle MOVX. Therefore, RAM access will not
be performed at full speed. This is a convenience to
existing designs that may not have fast RAM in place.
When maximum speed is desired, the software should
select a Stretch value of zero. When using very slow
RAM or peripherals, a larger stretch value can be
selected. Note that this affects data memory only and
the only way to slow program memory (ROM) access is
to use a slower crystal.
Using a Stretch value between one and seven causes
the microcontroller to stretch the read/write strobe and
all related timing. This results in a wider read/write
strobe allowing more time for memory/peripherals to
respond. The timing of the variable speed MOVX is
shown in the Electrical Specifications. Note that full
speed access is not the reset default case. Table 3
below shows the resulting strobe widths for each
Stretch value. The memory stretch is implemented
using the Clock Control Special Function Register at
SFR location 8Eh. The stretch value is selected using
bits CKCON.2–0. In the table, these bits are referred to
as M2 through M0. The first stretch (default) allows the
use of common 120 ns or 150 ns RAMs without dramati-
cally lengthening the memory access.
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PDF描述
DS80C323MCG Microprocessor
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相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
DS80C323-ENG 制造商:DALLAS 制造商全稱:Dallas Semiconductor 功能描述:High-Speed Microcontroller User Guide
DS80C323-ENL 制造商:DALLAS 制造商全稱:Dallas Semiconductor 功能描述:High-Speed Microcontroller User Guide
DS80C323-ENR 制造商:DALLAS 制造商全稱:Dallas Semiconductor 功能描述:High-Speed Microcontroller User Guide
DS80C323-FCD 制造商:DALLAS 制造商全稱:Dallas Semiconductor 功能描述:High-Speed Microcontroller User Guide
DS80C323-FCG 制造商:DALLAS 制造商全稱:Dallas Semiconductor 功能描述:High-Speed Microcontroller User Guide
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