GMS90C51 datasheet(14/59 Pages) HYNIX

14 / 59 page

GMS90 Series

Dec. 1998 Ver 3.0

ALE /

PROG

The Address Latch Enable / Program pulse

Output pulse for latching the low byte of the address

during an access to external memory. In normal

operation, ALE is emitted at a constant rate of 1/6 the

oscillator frequency, and can be used for external

timing or clocking. Note that one ALE pulse is skipped

during each access to external data memory. This pin

is also the program pulse input (PROG) during

EPROM programming.

In GMS9XC54/56/58:

If desired, ALE operation can be disabled by setting

bit 0 of SFR location 8EH. With this bit set, the pin is

weakly pulled high. The ALE disable feature will be

terminated by reset. Setting the ALE-disable bit has

no affect if the microcontroller is in external execution

mode.

EA / VPP

External Access Enable / Program Supply Voltage

EA must be external held low to enable the device to

fetch code from external program memory locations

0000H to FFFFH. If EA is held high, the device

executes from internal program memory unless the

program counter contains an address greater than its

internal memory size. This pin also receives the

12.75V programming supply voltage (VPP) during

EPROM programming.

Note;

however, that if any of the Lock bits are

programmed,

will

internally

latched on reset.

P0.0-P0.7

36-43

32-39

30-37

I/O

Port 0

Port 0 is an 8-bit open-drain bidirectional I/O port.

Port 0 pins that have 1s written to them float and can

be used as high-impedance inputs.

Port 0 is also the multiplexed low-order address and

data bus during accesses to external program and

data memory. In this application it uses strong internal

pull-ups when emitting 1s. Port 0 also outputs the

code

bytes

during

program

verification

the

GMS97X5X. External pull-up resistors are required

during program verification.

VSS

Circuit ground potential

VCC

Supply terminal for all operating modes

N.C.

1,12

23,34

-6,17

28,39

No connection

Symbol

Pin Number

Input/

Output

Function

PLCC-

PDIP-

MQFP-

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