Z86D990 Datasheet, PDF (43/102 Pages) Zilog, Inc. – Low-Voltage Micro controllers with ADC

Z86D990/Z86D991 OTP and Z86L99X ROM
Low-Voltage Microcontrollers with ADC
36
The counter/timer, prescaler, and associated mode registers are mapped into the
register file as shown in Figure 19. The software uses the counter/timer as a gen-
eral-purpose register, which eliminates the need for special instructions.
DEC
Hex identifiers
243
T1 prescaler
F3 PRE1
242
Timer/counter 1
F2 T1
241
Timer mode
F1 TMR
Figure 19. Register File
Prescaler and Counter/Timer
The prescaler PRE₁ (F3h) consists of an 8-bit register and a 6-bit down-counter as
shown in Figure 18 on page 35. The prescaler register is a read-write register.
Figure 20 shows the prescaler register.
R243 PRE1
Prescaler 1 Register
(F3h; Read/Write)
D₇ D₆ D₅ D₄ D₃ D₂ D₁ D₀
Figure 20. Prescaler 1 Register
Count mode
1 = T₁ modulo-N
0 = T₁ single pass
Clock source
1 = T₁ internal
0 = T₁ external (T_IN)
Prescaler modulo
(range: 1–64 decimal,
01h–00h)
PS003807-1002
PRELIMINARY