King Billion Electronics Co., Ltd

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HF88M02

January 16, 2004

Page 9 of 19

V1.11

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

i.e., key board is scanned using P0 and P1. When the execution of program returns to main loop after

interrupt service routine completed, the loading of address can still resume from where it was interrupted.

6.3 Sequential Read Mode and Auto Increment of Address Counter

With each read access to the ROM data (RS = “0xx”), the Address Counter is incremented automatically

by one with rising edge of OEn to facility sequential access to a block of ROM data and avoid repeated

loading of addresses.

6.4 Output data to External I/O

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

pin 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 expansion 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 0x00.

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

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) expansion 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 VDD or VSS if it is set

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