st62t25c STMicroelectronics, st62t25c Datasheet - Page 39

• Manufacturer Part Number: st62t25c
• Description: 8-bit Otp/eprom Mcus With A/d Converter, Oscillator Safeguard, Safe Reset And 28 Pins
• Manufacturer: STMicroelectronics

TIMER (Cont’d)
4.2.3 Application Notes
The user can select the presence of an on-chip
pull-up on the TIMER pin as option.
TMZ is set when the counter reaches zero; howev-
er, it may also be set by writing 00h in the TCR
register or by setting bit 7 of the TSCR register.
The TMZ bit must be cleared by user software
when servicing the timer interrupt to avoid unde-
sired interrupts when leaving the interrupt service
routine. After reset, the 8-bit counter register is
loaded with 0FFh, while the 7-bit prescaler is load-
ed with 07Fh, and the TSCR register is cleared.
This means that the Timer is stopped (PSI=“0”)
and the timer interrupt is disabled.
If the Timer is programmed in output mode, the
DOUT bit is transferred to the TIMER pin when
TMZ is set to one (by software or due to counter
decrement). When TMZ is high, the latch is trans-
parent and DOUT is copied to the timer pin. When
TMZ goes low, DOUT is latched.
A write to the TCR register will predominate over
the 8-bit counter decrement to 00h function, i.e. if a
write and a TCR register decrement to 00h occur
simultaneously, the write will take precedence,
and the TMZ bit is not set until the 8-bit counter
reaches 00h again. The values of the TCR and the
PSC registers can be read accurately at any time.
4.2.4 Timer Registers
Timer Status Control Register (TSCR)
Address: 0D4h — Read/Write
Bit 7 = TMZ: Timer Zero bit
A low-to-high transition indicates that the timer
count register has decrement to zero. This bit must
be cleared by user software before starting a new
count.
Bit 6 = ETI: Enable Timer Interrupt
When set, enables the timer interrupt request
(vector #3). If ETI=0 the timer interrupt is disabled.
If ETI=1 and TMZ=1 an interrupt request is gener-
ated.
Bit 5 = TOUT: Timers Output Control
When low, this bit selects the input mode for the
TIMER pin. When high the output mode is select-
ed.
TMZ
7
ETI
TOUT DOUT
PSI
PS2
PS1
PS0
0
Bit 4 = DOUT: Data Output
Data sent to the timer output when TMZ is set high
(output mode only). Input mode selection (input
mode only).
Bit 3 = PSI: Prescaler Initialize Bit
Used to initialize the prescaler and inhibit its count-
ing. When PSI=“0” the prescaler is set to 7Fh and
the counter is inhibited. When PSI=“1” the prescal-
er is enabled to count downwards. As long as
PSI=“0” both counter and prescaler are not run-
ning.
Bit 2, 1, 0 = PS2, PS1, PS0: Prescaler Mux. Se-
lect. These bits select the division ratio of the pres-
caler register.
Table 12. Prescaler Division Factors
Timer Counter Register TCR
Address: 0D3h — Read/Write
Bit 7-0 = D7-D0: Counter Bits.
Prescaler Register PSC
Address: 0D2h — Read/Write
Bit 7 = D7: Always read as “0”.
Bit 6-0 = D6-D0: Prescaler Bits.
D7
D7
7
7
PS2
0
0
0
0
1
1
1
1
D6
D6
D5
D5
PS1
1
0
0
1
1
0
0
1
D4
D4
ST62T15C/T25C/E25C
D3
D3
PS0
1
0
1
0
1
0
1
0
D2
D2
Divided by
D1
D1
128
16
32
64
8
1
2
4
39/70
D0
D0
0
0
39