AN2692 Freescale Semiconductor / Motorola, AN2692 Datasheet - Page 12

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

MC9S12NE64 Integrated Ethernet Controller
IIC Clock
The IIC bus is a two-wire, bidirectional serial bus that provides a simple, efficient method of data exchange
between two devices. The only clock source for the IIC module is the bus clock. The device is designed
to operate at speeds up to 100 kbps.
The IIC baud rate is a function of the bus clock divided by the SCL divider. Equation 8 shows how to
generate the SCL divider and illustrates the IIC frequency divider register (IICF) relationship to the SCL
divider variables.
Each of the variables in the SCL divider (MUL, SCI2tap, tap2tap, and SCL_TAP) can be derived from the
IICF IBCn bits.
The IIC baud rate is computed by Equation 9.
TIM Clock Rate
The only clock source for the TIM module is the bus clock. The TIM clock feeds into the three 4-channel
timers with 16-bit counters.
The TIM clock rate, R
prescaler includes the PR[2:0] bits of the TSCR2 register. The clock rate is computed by Equation 10.
ATD Conversion Clock Frequency
The only clock source for the analog-to-digital (ATD) module is the bus clock. The ATD clock source feeds
into a 16-channel ATD converter with 10-bit resolution and sets the ATD conversion clock frequency,
f
clock frequency will be in the range from 0.5 MHz to 2 MHz.
12
DesiredATD
Equation 8:
Equation 9:
Equation 10:
. Depending on the power supply voltage applied to the ATD converter, the ATD conversion
IIC baud rate =
SCL divider = mul × [2 × {2 + SCL2tap + ((SCL_TAP – 1) × tap2tap)}]
where: MUL = 2
DesiredTIM
SCL_TAP = 5 + IBC[2:0], if IBC[2:0] = 6, Tap = 12
tap2tap = 2
SCL2tap = (2
MC9S12NE64 Integrated Ethernet Controller, Rev. 0.2
R
, is a function of the bus clock divided by the timer prescaler. The timer
DesiredTIM
(mul × [2 × {2 + SCL2tap + (SCL_TAP – 1) × tap2tap)}]
IBC[7:6]
IBC[5:3]
IBC[5:3]
=
2
(PR[2:0])
f
– 2), if IBC[5:3] = 0, SCL2tap = 4
Bus
if IBC[2:0] = 7, Tap = 15
if IBC[5:3] = 1, SCL2tap = 4
if IBC[5:3] = 2, SCL2tap = 6
f
Bus
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