Z8F1233QH020SG Zilog, Z8F1233QH020SG Datasheet - Page 155

• Manufacturer Part Number: Z8F1233QH020SG
• Description: IC ENCORE XP MCU FLSH 12K 20QFN
• Manufacturer: Zilog
• Series: Encore!®r

Specifications of Z8F1233QH020SG

• Core Processor: Z8
• Core Size: 8-Bit
• Speed: 20MHz
• Peripherals: Brown-out Detect/Reset, LED, POR, PWM, WDT
• Number Of I /o: 17
• Program Memory Size: 12KB (12K x 8)
• Program Memory Type: FLASH
• Ram Size: 256 x 8
• Voltage - Supply (vcc/vdd): 2.7 V ~ 3.6 V
• Oscillator Type: Internal
• Operating Temperature: 0°C ~ 70°C
• Package / Case: 20-VQFN Exposed Pad, 20-HVQFN, 20-SQFN, 20-DHVQFN
• For Use With: 770-1002 - ISP 4PORT ZILOG Z8 ENCORE! MCU
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Eeprom Size: -
• Data Converters: -
• Connectivity: -
• Other names: 269-4656

PS025111-1207
Caution:
Clock Failure Detection and Recovery
Primary Oscillator Failure
The Z8F04xA family devices can generate non-maskable interrupt-like events when the
primary oscillator fails. To maintain system function in this situation, the clock failure
recovery circuitry automatically forces the Watchdog Timer Oscillator to drive the system
clock. The Watchdog Timer Oscillator must be enabled to allow the recovery. Although
this oscillator runs at a much slower speed than the original system clock, the CPU
continues to operate, allowing execution of a clock failure vector and software routines
that either remedy the oscillator failure or issue a failure alert. This automatic switch-over
is not available if the Watchdog Timer is the primary oscillator. It is also unavailable if the
Watchdog Timer Oscillator is disabled, though it is not necessary to enable the Watchdog
Timer reset function outlined in the Watchdog Timer chapter of this document.
The primary oscillator failure detection circuitry asserts if the system clock frequency
drops below 1 KHz ±50%. If an external signal is selected as the system oscillator, it is
possible that a very slow but non-failing clock can generate a failure condition. Under
these conditions, do not enable the clock failure circuitry (POFEN must be deasserted in
the OSCCTL register).
Watchdog Timer Failure
In the event of failure of a Watchdog Timer Oscillator, a similar non-maskable interrupt-
like event is issued. This event does not trigger an attendant clock switch-over, but alerts
the CPU of the failure. After a Watchdog Timer failure, it is no longer possible to detect a
primary oscillator failure. The failure detection circuitry does not function if the Watchdog
Timer is used as the primary oscillator or if the Watchdog Timer Oscillator has been
disabled. For either of these cases, it is necessary to disable the detection circuitry by
deasserting the WDFEN bit of the OSCCTL register.
The Watchdog Timer Oscillator failure detection circuit counts system clocks while
looking for a Watchdog Timer clock. The logic counts 8004 system clock cycles before
determining that a failure has occurred. The system clock rate determines the speed at
which the Watchdog Timer failure is detected. A very slow system clock results in very
slow detection times.
It is possible to disable the clock failure detection circuitry as well as all functioning
clock sources. In this case, the Z8 Encore!
can only be recovered by power-on-reset.
®
F0830 Series device ceases functioning and
Z8 Encore!
Product Specification
®
Oscillator Control
F0830 Series
145