Bit Path Definition Registers
82 – CIO Chip
VL-486-4 Reference Manual
Table 57: Register Bit Assignments
Bit
Mnemonic
Description
D7-D0
DD7-DD0
A 0 in a bit position of this register specifies the corresponding bit of the port
as an output bit, while a 1 specifies it as an input.
An input bit specification is overridden for bits in Port C used as outputs for
handshake signals or REQUEST/WAIT line.
A reset forces all bits in these registers to 0. All bits are read/write.
S
PECIAL
I/O C
ONTROL
R
EGISTERS
CIOASIC (READ/WRITE) 24H
CIOBSIC (READ/WRITE) 2CH
CIOCSIC (READ/WRITE) 07H
D7
D6
D5
D4
D3
D2
D1
D0
SC7
SC6
SC5
SC4
SC3
SC2
SC1
SC0
Each of the Special I/O Control registers is a dual-function register which specifies special
characteristics about its port's data path. Its exact function depends on the direction of data flow
defined for the path.
Table 58: Register Bit Assignments
Bit
Mnemonic
Description
D7-D0
SC7-SC0
If a bit is an input bit, a 1 in this register's corresponding bit position invokes a
1's catcher. A 1's catcher functions automatically latching a 1 if its input goes
to 1. It is cleared only by writing a 0 to the Input Data register. A 1's catcher is
inserted into the input path after the bit's invert/non-invert logic. If the bit is
programmed 0, it is a normal input bit. The 1's catcher is available only for
input bit port bits.
If a bit is an output bit, a 0 in the corresponding bit position of this register
specifies the output as a normal output with both a pull-up and a pull-down
transistor. A 1 in this register defined the output as open-drain; no pull-up
transistor is provided. The value programmed in this register applies to all
output modes, independent of utilization.
A reset forces all bits to 0. All bits are read/write.