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3.2.2 8255 Mode 0 Function Definitions
• Mode 0 of the 8255 provides simple input/output functions. No hand-
shaking is required since you read or write data directly to or from a
specified port.
• Six 8-bit ports (Port A0, B0, C0, A1, B1 and C1)
• Any port can be used for input or output
• Outputs are latched, whereas input are not latched
• The PCM-3724 requires ten I/O ports, identified below:
I/O Port Assignments
Location
BASE + 0
BASE + 1
BASE + 2
BASE + 3
BASE + 4
BASE + 5
BASE + 6
BASE + 7
BASE + 8
BASE + 9
Write
8255 Port A0
8255 Port B0
8255 Port C0
8255 Mode Register
for Ports A0, B0 & C0
8255 Port A1
8255 Port B1
8255 Port C1
8255 Mode Register
for Ports A1, B1 & C1
DIO direction
Gate control
17
Read
8255 Port A0
8255 Port B0
8255 Port C0
N/A
8255 Port A1
8255 Port B1
8255 Port C1
N/A
N/A
N/A
Chapter 3
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