HT47C20 datasheet(28/56 Pages) HOLTEK

28 / 56 page

HT47C20

January 18, 2000

Da t a B u s

WEA K

Pu l l - u p

PA0 / B Z

V DD

Ma s k

Op t i o n

V DD

BZ O p t i o n

R ead P a t h

B Z S i gnal

WEA K

Pu l l - u p

PA1 / B Z

V DD

Ma s k

Op t i o n

V DD

BZ O p t i o n

R ead P a t h

C h i p R es et

M a sk O p t i o n

S y s t em W ak e- up

M a sk O p t i o n

S y s t em W ak e- up

Da t a B u s

C h i p R es et

PA0/BZ, PA1/BZ input/output port

Input/output ports

There are 8-bit bidirectional input/output port

and 4-bit input port in the HT47C20, labeled PA

and PB which are mapped to the data memory

of [12H] and [14H] respectively. The high nibble

of the PA is NMOS output and input with

pull-high resisters. The low nibble of the PA can

be used for input/output or output operation by

selecting NMOS or CMOS output by mask op-

tion. Each bit on the PA can be configured as a

wake-up input, and the low nibble of the PA

with or without pull-high resistor by mask op-

tion. PB can only be used for input operation,

and each bit on the port can be configured with

pull high resistor by mask option. Both are for

the input operation, these ports are

non-latched, that is, the inputs should be ready

at the T2 rising edge of the instruction ²MOV A,

[m]² (m=12H or 14H). For PA output operation,

all data are latched and remain unchanged un-

til the output latch is rewritten.

When the structures of PA are open drain

NMOS type, it should be noted that, before

reading data from the pads, a ²1² should be

written to the related bits to disable the NMOS

device. That is done first before executing the

instruction ²MOV A, 0FFH² and ²MOV [12H],

A² to disable related NMOS device, and then

²MOV A, [12H]² to get stable data.

After chip reset, these input lines remain at a

high level or are left floating (by mask option).

Some instructions first input data and then fol-

low the output operations. For example, ²SET

[m].i², ²CLR [m].i², ²CPL [m]², ²CPLA [m]² read

the entire port states into the CPU, execute the

defined operations (bit-operation), and then

write the results back to the latches or to the ac-

cumulator. Each bit of the PA output latches

can not use these instruction, which may

change the input lines to output lines (when in-

put line is at low level).

HT47C20 Datasheet(PDF) 28 Page - Holtek Semiconductor Inc

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