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8XC196NT USER'S MANUAL
6.5.2
Configuring EPORT Pins
Each EPORT pin can be individually configured to operate either as an extended-address signal
or as an I/O pin in one of these modes:
•
complementary output (output only)
•
high-impedance input or open-drain output (input, output, or bidirectional)
6.5.2.1
Configuring EPORT Pins for Extended-address Functions
The EPORT pins default to their extended-address functions upon reset (see Table 6-19 on page
6-25 and Table B-6 on page B-14). During program execution, the pins can be reconfigured at
any time from address to I/O and back to address. However, this is not recommended unless you
understand the implications of changing memory addressing "on the fly." To change a pin from
I/O to address, clear the EP_REG.x bit and set the EP_MODE.x bit. (Clearing EP_REG.x is re-
quired for compatibility with software development tools.)
6.5.2.2
Configuring EPORT Pins for I/O
To configure a pin for I/O, write the appropriate values to the control registers, in this order:
1.
EP_DIR
2.
EP_MODE
3.
EP_REG
Table 6-18 lists the register settings for the EPORT pins.
Table 6-18. Configuration Register Settings for EPORT Pins
Desired Pin Configuration
Address
Complementary output
Open-drain output
Input
†
X = Don't care.
††
Must be zero for compatibility with software tools.
6-24
Configuration Register Settings
EP_DIR
EP_MODE
†
X
1
0
0
1
0
1
0
EP_PIN
Value
EP_REG
††
0
address
data value
data value
data value
data value
1
I/O pin value
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