King Billion Electronics Co., Ltd

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HF88M32B

January 16, 2004

9

V1.11

This specification is subject to change without notice. Please contact sales person for the latest version before use.

6.4.

Output data to External I/O

The device’s 16-bit Extension I/O capability provides additional I/O ports for applications where the I/O

pins are heavily used. To use as a certain pin as output pin, the corresponding bit in Direction Register

must be set to ‘1’. Please refer to the following example where output 0x00 to P0 to ‘0’ is intended.

1. Set RS to “101” (DIR0).

2. Keep D7 ~ D0 at 0xff (all bits in output mode).

3. Pulse the WEn to low then high to write to write contents of D-bus to DIR0.

4. Set RS to “100” (P0 Output Register).

5. Set D7 ~ D0 to 0x00.

6. Pulse the WEn to low then high to write contents of D-bus to P0 and drive all bits in P0 to low.

6.5.

Reading Input pin status

To use extension I/O ports as input pins and read the status from them, the corresponding bit in direction

register must be set to ‘0’. Please see the following example where reading inputs from of P1 is intended.

1. Set RS to “111” (DIR1).

2. Set D7 ~ D0 to 0x00h.

3. Pulse the WEn to low then high to set DIR1 to all High-Impedance input modes.

4. Set RS to “110” (P1 Output Register).

5. Pulse the OEn to low.

6. Read P1 then set the OEn back to high.

There is one thing should be noted. For any unused (open) extension I/O pin, it is advisable to set the port

to output mode either at ‘0’ or ‘1’ state to prevent it from floating or fix it at VCC or GND if it is set to

input mode. Otherwise, the noise might cause the unnecessary power consumption.

6.6.

Retrieving the Contents of Extension I/O registers

The contents of all four registers can be read through data bus. The ability to access the contents of

registers avoids the necessity of using the RAM as mirror to keep the current status of latches in

applications. However, extra care should be taken when reading P0 and P1. To read the contents of P0

and P1, the DIR0 and DIR1 should be set to output mode. Otherwise, the pin status instead of P0 and P1

will be read. The same precaution should be applied in Read-Modify-Write sequence that read back the

contents of the output latch of output mode pins and input status of input mode pins.

7. Timing Diagrams

Symbol

Parameter

Min.

Typ.

Max.

Unit

Chip selected to active width

0

50

-

ns