AN2692 Freescale Semiconductor / Motorola, AN2692 Datasheet - Page 13

• Manufacturer Part Number: AN2692
• Description: MC9S12NE64 Integrated Ethernet Controller
• Manufacturer: Freescale Semiconductor / Motorola

The ATD conversion clock frequency is a function of both the bus clock and an ATD prescaler value,
PRS[4:0]. The ATD conversion clock frequency can be calculated using Equation 11.
The PRS[4:0] bits are found in the ATD control register 4 (ATDCTL4). PRS[4:0] allows 32 prescaler
values to divide the bus clock. Based on the selected bus clock frequency and required system
conversion times, the user must choose the prescaler value to achieve the required ATD conversion
rate—keeping in mind the minimum and maximum ATD clock range.
RTI Time-Out Period
The real-time interrupt (RTI) function can be used to generate a hardware interrupt at a fixed periodic rate,
f
The RTI prescaler is controlled using the CRG RTI control register (RTICTL). This register controls the
two RTI frequency divide rate components. The RTI prescaler rate select bits (RTR[6:4]) and the RTI
modulus counter select bits (RTR[3:0]) are combined to determine the overall RTI frequency divide rate.
Use Equation 12 to calculate the RTI periodic rate.
Note that if RTR[6:4] is equal-to zero, the RTI is disabled. In SCM mode, the RTI operates using f
COP Time-Out Period
The computer operating properly (COP) is a free-running watchdog timer. It enables the user to check
whether a program is running and sequencing correctly. Like the RTI, the COP runs with a gated oscillator
clock, OSCCLK. Three control bits, CR[2:0], in the COPCTL register allow the selection of seven COP
timeout periods, t
Special cases:
Note that if COP[2:0] is equal-to zero, the RTI is disabled. In SCM mode, the RTI operates using f
Freescale Semiconductor
DesiredRTI
•
•
Equation 11:
Equation 12:
Equation 13:
if CR[2:0] = 6, t
if CR[2:0] = 7, t
. The RTI runs with a gated oscillator clock, OSCCLK. OSCCLK feeds into an RTI prescaler.
DesiredCOP
DesiredCOP
DesiredCOP
. Use Equation 13 to calculate t
f
DesiredRTI
MC9S12NE64 Integrated Ethernet Controller, Rev. 0.2
t
DesiredCOP
= t
= t
Bus
Bus
f
DesiredATD
=
× 2
× 2
(23)
(24)
= t
(RTR[3:0] + 1) × (2
Bus
=
× 2
2 × (PRS[4:0] + 1)
(12 + 2 × CR[2:0])
f
BUS
f
Bus
DesiredCOP
(9 + RTR[6:4])
MC9S12NE64 Integrated Ethernet Controller
. Note the special cases provided.
)
SCM
SCM
.
.
13