Z86D990 Datasheet, PDF (74/102 Pages) Zilog, Inc. – Low-Voltage Micro controllers with ADC

Z86D990/Z86D991 OTP and Z86L99X ROM
Low-Voltage Microcontrollers with ADC
67
Port Configuration Registers (P456CON and P3M)
The port configuration register (described in Table 24) switches the comparator
inputs from digital to analog and allows Ports 4, 5, and/or 6 to be switched from
push/pull active outputs to open drain outputs. In ZiLOG Test Mode, bit 3 of this
register is used to enable the Address Strobe/Data Strobe. Bit 3 is not available in
User Mode.
Table 24. P456CON Register (Group/Bank 0Fh, Register 0)
Bit
7
6
5
4
3
2
1
0
Bit/Field Not Used
P51_ P52_
P6_
P5_
P4_
Mode Mode Reserved Output Output Output
R/W
R/W R/W R/W R/W R/W
W
W
W
Reset
0
0
0
0
0
1
1
1^†
R = Read, W = Write, X = Indeterminate
Bit
Position
Bit/Field
R/W Value Description
76______ Not Used
R/W
These bits exist but do not have any
function assigned to them; they are
reserved for future extensions and must
not be used.
__5_____ Comparator 1 R/W 1
Mode
0
Analog (P50, P51 as Inputs)
Digital inputs
___4____ Comparator 2 R/W 1
Mode
0
Analog comparator inputs (P52, P53
configured as Inputs)
Digital inputs
____3___ Reserved
_____2__ Port 6 Output W 1
Configuration
0
Push-Pull Active
Open Drain Outputs
Always reads back 1*
______1_ Port 5 Output W 1
Configuration
0
Push-Pull Active
Open Drain Outputs
Always reads back 1*
_______0 Port 4 Output W 1
Configuration
0
Push-Pull Active
Open Drain Outputs
Always reads back 1*^†
Note: *Do not use the read-modify-write instructions (for example, OR and AND) with this register.
Bits 0, 1, and 2 always read back 1.
Note: ^†For Z86L990/L991, P43 can never be configured as push-pull. After any reset, P43 is
configured as tristate high impedance.
Port 2 outputs are configured using the P3M Register, shown in Table 25. Bit 0 of
the P3M Register switches Port 2 from push/pull active to open drain outputs. No
other bits in this register are implemented.
PS003807-1002
PRELIMINARY