Z8 Encore! XP® 4K Series
Product Specification
43
functions as GPIO. If enabled, select one of four alternate functions using alternate func-
tion set subregisters 1 and 2 as described in the Port A–D Alternate Function Set 1 Sub-
Registers on page 45 and Port A–D Alternate Function Set 2 Sub-Registers on page 46.
Refer to the GPIO Alternate Functions on page 33 to determine the alternate function asso-
ciated with each port pin.
Caution:
Do not enable alternate functions for GPIO port pins for which there is no
associated alternate function. Failure to follow this guideline can result in
unpredictable operation.
Table 21. Port A–D Alternate Function Sub-Registers (PxAF)
BITS
7
6
5
4
3
2
1
0
AF7
AF6
AF5
AF4
AF3
AF2
AF1
AF0
FIELD
RESET
R/W
00H (Ports A–C); 01H (Port D); 04H (Port A of 8-pin device)
R/W
If 02H in Port A–D Address Register, accessible through the Port A–D Control Register
ADDR
AF[7:0]—Port Alternate Function enabled
0 = The port pin is in normal mode and the DDxbit in the Port A–D Data Direction sub-
register determines the direction of the pin.
1 = The alternate function selected through Alternate Function Set sub-registers is
enabled. Port pin operation is controlled by the alternate function.
Port A–D Output Control Sub-Registers
The Port A–D Output Control sub-register (Table 22) is accessed through the Port A–D
Control register by writing 03Hto the Port A–D Address register. Setting the bits in the
Port A–D Output Control sub-registers to 1 configures the specified port pins for open-
drain operation. These sub-registers affect the pins directly and, as a result, alternate func-
tions are also affected.
Table 22. Port A–D Output Control Sub-Registers (PxOC)
BITS
7
6
5
4
3
2
1
0
POC7
POC6
POC5
POC4
POC3
POC2
POC1
POC0
FIELD
RESET
R/W
0
0
0
0
0
0
0
0
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
If 03H in Port A–D Address Register, accessible through the Port A–D Control Register
ADDR
POC[7:0]—Port Output Control
These bits function independently of the alternate function bit and always disable the
PS022815-0206
General-Purpose I/O
ZILOG [ ZILOG, INC. ]
