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M37640E8

Single-Chip 8-BIT CMOS Microcontroller M37640E8-XXXFP Specification

MITSUBISHI ELECTRIC  

Mitsubishi Microcomputer

7600 Series

M37640E8-XXXF Preliminary Specification

2.5.6 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

(P71) and HLDA (P73). 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 P37 (RD) and port P36 (WR) high. Ports

P37 and P36 are held high to prevent 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 P34 (Φout)

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 P1, P2, P37 and P36 will begin to drive the external

buses again. The timing for the hold function is shown in Figure 2-20. 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 IBF1 pin functionality is used.

XIN

P1

P2

P1PER

P2PER

Φout

RD, WR

ADDRout

DATAin/out

HOLD

HLDA

tsu(HOLD-Φout)

th(Φout-HOLD)

td(Φout-HLDA)

td(Φout-HLDA)

Figure 2-20. Hold Mode Timing Diagram

2.5.7 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 instructions LDA (IndY) and STA (IndY) Port 40 (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 representing AB16 and the other AB17. The instruction sequences for STA (IndY) and LDA

(IndY) are shown in Figure 2-21. and Figure 2-22.

Processor Modes

7/9/98

2-23

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