z8e001 ZiLOG Semiconductor, z8e001 Datasheet - Page 27

• Manufacturer Part Number: z8e001
• Description: Feature-rich Z8plus One-time Programmable Otp Microcontroller
• Manufacturer: ZiLOG Semiconductor

ZiLOG
Each 8-bit timer is provided a pair of registers, which are
both readable and writable. One of the registers is defined
to contain the auto-initialization value for the timer, while
the second register contains the current value for the timer.
When a timer is enabled, the timer decrements whatever
value is currently held in its count register, and then con-
tinues decrementing until it reaches 0. At this time, an in-
terrupt is generated and the contents of the auto-initializa-
tion register optionally copy into the count value register.
If auto-initialization is not enabled, the timer stops counting
upon reaching 0, and control logic clears the appropriate
control register bit to disable the timer. This operation is re-
ferred to as Òsingle-shotÓ. If auto-initialization is enabled,
the timer continues counting from the initialization value.
Software should not attempt to use registers that are defined
as having timer functionality.
Software is allowed to write to any register at any time, but
care should be taken if timer registers are updated while the
timer is enabled. If software updates the count value while
the timer is in operation, the timer continues counting based
upon the software-updated value.
DS001101-Z8X0400
0C0
D7
Note: Timer T01 is a 16-bit PWM Timer formed by cascading 8-bit timers
D6
D5
T1 (MSB) and T0 (LSB). T23 is a standard 16-bit timer formed
by cascading 8-bit timers T3 (MSB) and T2 (LSB).
D4
TCTLLO
D3
Figure 22. TCTLLO Register
D2
P R E L I M I N A R Y
D1
Note: Strange behavior can result if the software update oc-
Similarly, if software updates the initialization value reg-
ister while the timer is active, the next time that the timer
reaches 0, it initializes using the updated value.
Note: Strange behavior could result if the initialization value
Whether initialization is done with the new or old value is
a function of the exact timing of the write operation. In all
cases, the Z8E001 prioritizes the software write above that
of a decrementer writeback; however, when hardware
clears a control register bit for a timer that is configured for
single-shot operation, the clearing of the control bit over-
rides a software write. Reading either register can be done
D0
curred at exactly the point that the timer was reaching 0
to trigger an interrupt and/or reload.
register is being written while the timer is in the process
of being initialized.
D2 D1 D0
---- ---- --- ------------ ------------ ---------------
0
0
0
0
1
1
1
1
(NOTE: (*) INDICATES AUTO-RELOAD
RESERVED (MUST BE 0)
1 = T23 16-BIT TIMER ENABLED WITH
0 = T2 AND T3 TIMERS DISABLED
IS ACTIVE.)
RESERVED (MUST BE 0)
0 0 DISAB.
0 1 ENAB.
1 0 DISAB.
1 1 ENAB.
0 0
0 1 ENAB.(*) DISAB.
1 0 DISAB.
1 1 ENAB.(*) ENAB.(*)
AUTO-RELOAD ACTIVE
T0
TIMER STATUS
DISAB.
DISAB.
ENAB.
ENAB.
Z8Plus OTP Microcontroller
ENAB.(*)
T1
ENAB.(*)
T01
Z8E001
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