
Functional Description
Copyright 1999-2002 by LSI Logic Corporation. All rights reserved.
53 of 118
April, 2002
2.25.4 Bit Types
Since the serial port is bidirectional, there are many types of bits. The bit
type definitions are summarized in
Table 7
.
Write bits (W) are inputs during a write cycle and are high impedance
during a read cycle. Read bits (R) are outputs during a read cycle and
high impedance during a write cycle. Read/Write bits (R/W) are actually
write bits that can be read out during a read cycle. R/WSC bits are R/W
bits that are self-clearing after a set period of time or after a specific
event has completed. R/LL bits are read bits that latch themselves when
they go low, and they stay latched low until read. After they are read, they
are reset high. R/LH bits are the same as R/LL bits, except that they latch
high. R/LT are read bits that latch themselves whenever they make a
transition or change value, and they stay latched until they are read. After
R/LT bits are read, they are updated to their current value. The R/LT bits
can also be programmed to assert the interrupt function as described in
the Interrupt section.
Table 7
MI Register Bit Type Definition
Sym.
Name
Definition
Write Cycle
Read Cycle
W
Write
Input
No Operation, Hi Z
R
Read
No Operation, Hi Z
Output
R/W
Read/Write
Input
Output
R/WSC
Read/Write
Self Clearing
Input. Clears Itself After
Operation Completed
Output
R/LL
Read/Latching
Low
No Operation, Hi Z
Output. When bit goes low, bit latched.
When bit is read, bit updated.
R/LH
Read/Latching
High
No Operation, Hi Z
Output. when bit goes high, bit latched.
When bit is read, bit updated.
R/LT
Read/Latching on
Transition
No Operation, Hi Z
Output. When bit transitions, bit latched
and interrupt set. When bit is read, inter-
rupt cleared and bit updated.