20-668-0003 Rabbit Semiconductor, 20-668-0003 Datasheet - Page 120

• Manufacturer Part Number: 20-668-0003
• Description: IC CPU RABBIT2000 30MHZ 100PQFP
• Manufacturer: Rabbit Semiconductor

Specifications of 20-668-0003

• Processor Type: Rabbit 2000 8-Bit
• Speed: 30MHz
• Voltage: 2.7V, 3V, 3.3V, 5V
• Mounting Type: Surface Mount
• Package / Case: 100-MQFP, 100-PQFP
• Data Bus Width: 8 bit
• Maximum Clock Frequency: 30 MHz
• Operating Supply Voltage: 0 V to 5.5 V
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Minimum Operating Temperature: - 40 C
• Number Of Programmable I/os: 40
• Number Of Timers: 8 & 10 bit
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Features: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• Other names: 20-668-0003; 316-1062

The control register (TACR) is laid out as shown in Table 11-3.
The time constant register for each timer is simply an 8-bit data register holding a number
between 0 and 255. The time constant registers are write only.
11.1.2 Practical Use of Timer A
Timer A is disabled (bit 0 in control and status register) on power-up. Timer A is normally
set up while the clock is disabled, but the timer setup can be changed while the timer is
running when there is a need to do so. Timers that are not used should be driven from the
output of A1 and the reload register should be set to 255. This will cause counting to be as
slow as possible and consume minimum power.
Timer A has five separate subtimer units, A1 and A4–A5, that are also referred to as timers.
Most likely, if a serial port is going to be used and a timer is needed to provide the baud
clock, that timer will be set up to be driven directly from the clock, and the interrupt asso-
ciated with that timer will be disabled. (Serial port interrupts are generated by the serial
port logic.)
The value in the reload register can be changed while the timer is running to change the
period of the next timer cycle. When the reload register is initialized, the contents of the
countdown counter may be unknown, for example, during power-up initialization. If inter-
rupts are enabled, then the first interrupt may take place at an unknown time. Similarly, if
the timer output is being used to drive the clock for a parallel port or serial port, the first
clock may come at a random time. If a periodic clock is desired, it is probably not impor-
tant when the first clock takes place unless a phase relationship is desired relative to a dif-
ferent timers.
A phase relationship between two timers can be obtained in several ways. One way is to
set both reload registers to zero and to wait long enough for both timers to reload (maxi-
mum 256 clocks). Then both timers’ reload registers can be set to new values before or
after both are clocked.
114
Source A7
0-pclk/2
1-A1
Bit 7
A7
Source A6
0-pclk/2
1-A1
Bit 6
A6
Table 11-3. Timer A Control Register (adr = 0x0A4)
Source A5
0-pclk/2
1-A1
Bit 5
A5
Source A4
0-pclk/2
1-A1
Bit 4
A4
not used
ignored
Bits 3, 2
Rabbit 2000 Microprocessor User’s Manual
00—Interrupt disabled
01—Enable priority 1 interrupt
10—Enable priority 2 interrupt
11—Enable priority 3 interrupt
Bits 1, 0