PC87392 datasheet(87/148 Pages) NSC

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5.0 Game Port (GMP) (Continued)

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5.2.5

Operation Control

When the Game Port is operated in Legacy mode, it can only be operated by polling (see Section 5.2.4,

Legacy Mode).

When the Game Port is operated in Enhanced mode, both kinds of status reading operations (position and button) can be

performed using polling or interrupt controlled operation.

If polling controlled operation is preferred, the software should poll either the GMPLST register for the direct status of the

buttons as in Legacy mode, or the GMPXST register which provides indications regarding button events detected by hard-

ware. The GMPXST register should also be polled for the status of the position counters. When the status is ready, the

counter values can be read. These values reflect the positions indicated by the game device.

If interrupt controlled operation is preferred, the software should first define the events on which an interrupt request is to be

issued. This is done by writing the required values to the GMPEPOL (see Section 5.3.14) and GMPIEN (see Section 5.3.5)

registers. The GMPEPOL register defines the events on which the buttons cause an interrupt request to be issued. These

events are all edge-triggered. The GMPIEN register determines what events are physically routed to the interrupt request

assigned to the Game Port. An independent interrupt enable bit is implemented in the GMPIEN register for each one of the

four buttons and two position counters of the two supported game devices.

5.3

GAME PORT REGISTERS

The following abbreviations are used to indicate the Register Type:

R/W = Read/Write

R = Read from a speciﬁc address returns the value of a speciﬁc register. Write to the same address is to a different

W=Write

RO = Read Only

R/W1C = Read/Write 1 to Clear. Writing 1 to a bit clears it to 0. Writing 0 has no effect.

5.3.1

Game Port Register Map

The following table lists the Game Port registers. for the Game Port register bitmap, see Section 5.4.

Offset

Mnemonic

Type

Section

00h

GMPCTL Game Port Control

R/W

5.3.2

01h

GMPLST

Game Port Legacy Status

5.3.3

02h

GMPXST Game Port Extended Status

R/W1C

5.3.4

03h

GMPIEN

Game Port Interrupt Enable

R/W

5.3.5

04h

GMPAXL

Game Device A X Position Low Byte

5.3.6

05h

GMPAXH Game Device A X Position High Byte

5.3.7

06h

GMPAYL

Game Device A Y Position Low Byte

5.3.8

07h

GMPAYH

Game Device A Y Position High Byte

5.3.9

08h

GMPBXL Game Device B X Position Low Byte

5.3.10

09h

GMPBXH Game Device B X Position High Byte

5.3.11

0Ah

GMPBYL Game Device B Y Position Low Byte

5.3.12

0Bh

GMPBYH Game Device B Y Position High Byte

5.3.13

0Ch

GMPEPOL Game Port Event Polarity

R/W

5.3.14

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