Port B; Full Interrupt Request Multiplexer - Motorola MC68340 User Manual

4.2.5.2 PORT B. Port B pins can be independently programmed to function as chip
selects, IRQ and MODCK pins, or discrete I/O pins. These pins are multiplexed as
shown in Figure 4-7. Selection of a pin function is accomplished by a combination of the
port B pin assignment register (PPARB) and the FIRQ bit of the MCR. See Table 4-5 for
port B combinations. By changing the value of the FIRQ bit and the corresponding bits in
the PPARB for a particular signal, the port B pins can be configured for different pin
functions. Upon reset, port B is configured as MODCK, IRQ7, IRQ6, IRQ5, IRQ3 , and
CS3–CS0 .
Signal
IRQ7
IRQ6
IRQ5
IRQ3
CS3
CS2
CS1
CS0
MODCK
NOTE: MODCK has no function after reset.
4-16
Freescale Semiconductor, Inc.
INTERRUPT
PORT
LOGIC
IRQ4/PORT B4
IRQ2/PORT B2
IRQ1/PORT B1
AVEC
CS3
CS2
CHIP-
SELECT
CS1
MODULE
CS0
FIRQ
Figure 4-7. Full Interrupt Request Multiplexer
Table 4-5. Port B Pin Assignment Register
FIRQ = 0 FIRQ = 0
PPARB = 0 PPARB = 1
IRQ7
PORTB7
PORTB6 IRQ6
IRQ5
PORTB5
PORTB3 IRQ3
CS3 CS3
CS2 CS2
CS1 CS1
CS0 CS0
PORTB0 MODCK
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MODCK/PORT B0
IRQ7/PORT B7
IRQ6/PORT B6
IRQ5/PORT B5
IRQ3/PORT B3
CS3/IRQ4/PORT B4
CS2/IRQ2/PORT B2
FULL IRQ
CS1/IRQ1/PORT B1
MUX
CS0/AVEC
Pin Function
FIRQ = 1
PPARB = 0
PORTB7
PORTB6
PORTB5
PORTB3
PORTB4
PORTB2
PORTB1
AVEC
PORTB0
FIRQ = 1
PPARB = 1
IRQ7
IRQ6
IRQ5
IRQ3
IRQ4
IRQ2
IRQ1
AVEC
MODCK
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