參數(shù)資料
型號(hào)： M37640E8FP
廠商： Mitsubishi Electric Corporation
英文描述： SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER
中文描述： 單芯片8位CMOS微機(jī)
文件頁(yè)數(shù)： 14/96頁(yè)
文件大小： 1477K
代理商： M37640E8FP
14
Ver 1.4
MITSUBISHI MICROCOMPUTERS
7640 Group
SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER
1.12.5 Hold Function
The hold function is used when the MCU is put in a
system where more than one device will need control
of the external address and data buses. Two signals
are used to implement this function, HOLD (P7
1
) and
HLDA (P7
3
). HOLD is an input to the MCU and is
brought low when an external device wants the MCU
to relinquish the address and data buses. HLDA is an
output from the MCU that signals when the MCU has
relinquished the buses. When this is the case, the
MCU tri-state ports 0 and 1 (address bus) and port 2
(data bus), and holds port P3
7
(RD) and port P3
6
(WR) high. Ports P3
7
and P3
6
are held high to pre-
vent any external device that is enabled by RD or WR
from being falsely activated. The clocks to the CPU
are stopped, but the peripheral clocks and port P3
4
(
out
) continue to oscillate. HOLD is brought high to
allow the MCU to regain the address and data buses.
When this occurs, HLDA will go high and ports P
1
, P
2
,
P3
7
and P3
6
will begin to drive the external buses
again. The timing for the hold function is shown in Fig-
ure 1.12. The hold function is only valid for memory
expansion and microprocessor modes. Bit 5 of CPMB
is used to enable the hold function. HLDA will loose
its function when the IBF
1
pin functionality is used.
1.12.6 Expanded Data Memory Access
The Expanded Data Memory Access (EDMA) mode
feature allows the user to access a greater than 64
Kbyte data area for instructions LDA (IndY) with T=“0”
and T=“1”, and STA (IndY). Bit 4 of CPMB is used to
enable/disable the EDMA function. If bit 4 of CPMB
equals “1”, then during the data read/write cycle of in-
structions LDA (IndY) and STA (IndY) Port 4
0
(EDMA)
is driven low. The EDMA signal output can be used by
an external decoder to indicate when the read/write is
to a different 64 Kbyte bank. The actual determination
of which bank to access can be done by using a few
bits of a port to represent the extended addresses
above AB15. For example, if four banks are accessed,
then two bits are needed to uniquely identify each
bank. Two port bits can be used for this, one repre-
senting AB16 and the other AB17. The instruction
sequences for STA (IndY) and LDA (IndY) are shown in
Figure 1.13 and Figure 1.14.
Fig. 1.12. Hold Function Timing Diagram
X
IN
Φ
out
RD, WR
ADDR
out
DATA
in/out
HOLD
HLDA
t
su
(HOLD-
Φ
out
)
t
h
(
Φ
out
-HOLD)
t
d
(
Φ
out
-HLDA)
t
d
(
Φ
out
-HLDA)
------
------
------
------
------
////////
////////
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