Rainbow Electronics ATAR862-3 - Manual (Page 46)

46
ATAR862-3
4556B–4BMCU–02/03
Mode 3/4: 8-bit Compare
Counter and 4-bit
Programmable Prescaler Figure 40. 4-/8-bit Compare Counter
In these modes the 4-bit and the 8-bit counter stages work independently as a 4-bit
prescaler and an 8-bit timer with an 2-bit prescaler or as a duty cycle generator. Only in
the mode 3 and mode 4, can the 8-bit counter be supplied via the external clock input
(T2I) which is selected via the P4CR register. The 4-bit prescaler is started via activating
of mode 3 and stopped and reset in mode 4. Changing mode 3 and 4 has no effect for
the 8-bit timer stage. The 4-bit stage can be used as prescaler for Timer 3, the SSI or to
generate the stop signal for modulator 2 and modulator 3.
Timer 2 Output Modes The signal at the timer output is generated via modulator 2. In the toggle mode, the com-
pare match event toggles the output T2O. For high resolution duty cycle modulation 8
bits or 12 bits can be used to toggle the output. In the duty cycle burst
modulator modes
the DCG output is connected to T2O and switched on and off either by the toggle flipflop
output or the serial data line of the SSI. Modulator 2 also has 2 modes to output the con-
tent of the serial interface as Biphase or Manchester code.
The modulator output stage can be configured by the output control bits in the T2M2
register. The modulator is started with the start of the shift register (SIR = 0) and
stopped either by carrying out a shift register stop (SIR = 1) or compare match event of
stage 1 (CM1) of Timer 2. For this task, Timer 2 mode 3 must be used and the prescaler
has to be supplied with the internal shift clock (SCL).
Figure 41. Timer 2 Modulator Output Stage
4-bit counter
4-bit compare
RES
4-bit register
8-bit counter
8-bit compare
8-bit register
OVF2
CM2
RES
T2RM T2OTM
Timer 2
output mode
and T2OTM-bit
T2IM T2CTM
TOG2
INT4
CL2/2
DCG
T2D1, 0
DCGO
P41M2, 1 P4CR
CM1 POUT
CL2/1
MUX
TOG3
T1OUT
SYSCL
SCL
T2CS1, 0
SYSCL
T2I
Toggle
RES/SET
Biphase/
Manchester
modulator
T2TOP T2OS2, 1, 0 T2M2
T2O
M2
M2
S1
S2
S3
Modulator3
RE
FE
OMSK
SSI
CONTROL
TOG2
SO
DCGO