Alternate Pin Functions
MOTOROLA
MC68322 USER’S MANUAL
D-3
The registers in the following table have been added for buzzer control.
D.4 INPUT PIN MODE
For A[22:25] to be programmed as input pins, they must be three-stated on power-up to
prevent the processor from driving them during the initial bus cycles, which could cause bus
contention on these lines. To accommodate this condition, A[22:25] will power-up in a
three-state mode when a special state of the HI-Z and TEST pins exists. The normal
functions for BR and DREQ will also be disabled in input pin mode (ALTPIN SEL register
bits 14,15 are set). The table below shows the modes for these pins.
D.5 BUZZER
The BG output pin now has a buzzer control function, which consists of an 8-bit interval
control register, a 1-bit enable register, and a 16-bit free-running counter. The eight bits in
the BUZZER INT register control the value to be loaded into the upper byte of the 16-bit
counter after it reaches a count of zero. The lower byte will always be loaded with $FF. The
enable bit in the BUZZER ENB register causes the output from the BG pin to toggle every
time the counter reaches zero. The buzzer function drives a buzzer on the board or front
panel. On products that need this feature, the buzzer control function saves a 555 chip with
its resistors and capacitors.
D.6 IN-CIRCUIT EMULATION
If the alternate pin function is to be used in a system, then an in-circuit emulator (ICE) cannot
be used for system development. This feature of the G59B Mask Set is not available in an
ICE version. If the alternate pin function will not be used in the system, then the original ICE
version of the MC68322 can be used with an in-circuit emulator.
REGISTER
ADDRESS
BITS
R/W
DESCRIPTION
BUZZER INT
00FFF608
8
R/W
Buzzer Interval.
BUZZER ENB
00FFF60A
1
R/W
Buzzer Enable.
HI-Z
TEST
FUNCTION
0
Three-State All Outputs
0
1
Input Pin Mode, A[22:25] Three-Stated
ALTPIN SEL Register Bits 0-3, 14-15 = 1
1
0
Normal Mode, A[22:25] Enabled
ALTPIN SEL Register Bits 0-15 = 0
1
Special Test Mode (Do Not Use)
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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