Z8F1680SH020SG Datasheet, PDF (74/412 Pages) Zilog, Inc. – High-Performance 8-Bit Microcontrollers

Z8 Encore! XP^® F1680 Series
Product Specification
49
7.9. External Clock Setup
For systems using an external TTL drive, PB3 is the clock source for 20-pin, 28-pin, 40-
pin and 44-pin devices. In this case, configure PB3 for alternate function CLKIN. Write to
the Oscillator Control Register (see page 320) such that the external oscillator is selected
as the system clock.
Table 17. Port Alternate Function Mapping, 20-Pin Parts^1,2
Port
Pin Mnemonic
Alternate Function Description
Alternate Function
Set Register AFS1
Port A PA0 T0IN/T0OUT
Timer 0 Input/Timer 0 Output
Complement
AFS1[0]: 0
Reserved
AFS1[0]: 1
PA1 T0OUT
Timer 0 Output
AFS1[1]: 0
Reserved
AFS1[1]: 1
PA2 DE0
UART 0 Driver Enable
AFS1[2]: 0
Reserved
AFS1[2]: 1
PA3 CTS0
UART 0 Clear to Send
AFS1[3]: 0
Reserved
AFS1[3]: 1
PA4 RXD0/IRRX0
UART 0/IrDA 0 Receive Data
AFS1[4]: 0
T2IN/T2OUT
Timer 2 Input/Timer 2 Output
Complement
AFS1[4]: 1
PA5 TXD0/IRTX0
UART 0/IrDA 0 Transmit Data
AFS1[5]: 0
T2OUT
Timer 2 Output
AFS1[5]: 1
PA6 T1IN/T1OUT
SCL
Timer 1 Input/Timer 1 Output
Complement
I²C Serial Clock
AFS1[6]: 0
AFS1[6]: 1
PA7 T1OUT
SDA
Timer 1 Output
I²C Serial Data
AFS1[7]: 0
AFS1[7]: 1
Notes:
1. Because there are at most two choices of alternate functions for some pins in Port A, the Alternate Function Set
Register (AFS2) is implemented but not used to select the function. The alternate function selection must also
be enabled, as described in the Port A–E Alternate Function Subregisters section on page 61.
2. Because there is only one alternate function for each Port D pin, the Alternate Function Set registers are not
implemented for Port D. Enabling the alternate function selections automatically enables the associated alter-
nate function, as described in the Port A–E Alternate Function Subregisters section on page 61.
PS025015-1212
PRELIMINARY
General-Purpose Input/Output