Z86D990 Datasheet, PDF (44/102 Pages) Zilog, Inc. – Low-Voltage Micro controllers with ADC

Z86D990/Z86D991 OTP and Z86L99X ROM
Low-Voltage Microcontrollers with ADC
37
The six most significant bits (D₂–D₇) of PRE₁ hold the prescaler count modulo, a
value from 11 to 64 decimal. The prescaler register also contains control bits that
specify T₁ counting modes. These bits also indicate whether the clock source for
T₁ is internal or external.
The counter/timer T₁ (F2h) consists of an 8-bit down-counter, a write-only register
that holds the initial count value, and a read-only register that holds the current
count value (see Figure 18 on page 35). The initial value can range from 1 to 256
decimal (01h, 02h, ..., 00h). Figure 21 illustrates the counter/timer register.
R242 T1
Counter/Timer 1 Register
(F2h; Read/Write)
D₇ D₆ D₅ D₄ D₃ D₂ D₁ D₀
Figure 21. Counter/Timer 1 Register
Initial value when written
(range 1–256 decimal, 01h–00h)
Current value when read
Counter/Timer Operation
Under software control, T₁ is started and stopped using the Timer Mode register
(F1h) bits D₂–D₃: a Load bit and an Enable Count bit. See Figure 22.
R241 TMR
Timer Mode Register
(F1h; Read/Write)
D₃ D₂ D₁ D₀
Figure 22. Timer Mode Register
Reserved
0 = No function
1 = Load T₁
0 = Disable T₁ count
1 = Enable T₁ count
PS003807-1002
PRELIMINARY