Motorola MPC823e User Manual

Clocks and Power Control
5-22 MPC823e REFERENCE MANUAL MOTOROLA
CLOCKS AND POWER
5
CONTROL
5.3.5 Clock Configuration
You can configure the clock of the MPC823e using the MODCK1 and MODCK2 pins. The
SPLL has several power and ground pins (VDDSYN, VSSSYN, VSSSYN1, and XFC) that
must be properly terminated for stability and CLKOUT integrity.
5.3.5.1 MODE CLOCK PINS. The MODCK1 and MODCK2 pins are used to determine
clock source and configuration options. These pins are sampled on the rising edge of the
PORESET
pin. MODCK1 specifies the input source to the SPLL and, combined with
MODCK2, specifies the multiplication factor at reset. If you do not want the PITRTCLK,
TMBCLK, and multiplication factor to change during power-down mode, do not sample the
MODCK1 and MODCK2 pins during wake-up. Thus, the PORESET
pin must remain
negated while the HRESET
pin is asserted during this wake-up sequence.
MODCK1 selects the clock source to use (EXTCLK or main oscillator) and MODCK2 selects
the reference frequency (4MHz, 32kHz, or EXTCLK). If, during the power-on reset
sequence, the MODCK1 pin is zero, then the oscillator’s 4MHz or 32kHz clock is the
selected input. If MODCK1 is one, then the EXTCLK pin is the input source to the SPLL. The
system clock frequency (GCLK1) can be divided as defined by the DFNH and DFNL fields
in the SCCR. The maximum system clock frequency occurs when the DFNH field is equal
to 00. If MODCK2 is zero during the power-on reset sequence, the input frequency is either
32kHz or EXTCLK (one-to-one mode). If the MODCK2 pin is one, then a 4MHz clock is the
input source to the SPLL.
If the EXTCLK pin is the main timing reference and the OSCM is the timing reference to the
real-time clock and periodic interrupt timer, then the frequency of the OSCM must be 32.768
or 38.4kHz. Depending on how the TBS bit is set in the SCCR, the timebase clock is either
the SPLL clock frequency or GCLK2. The RTSEL field in the SCCR specifies the source
(EXTCLK or OSCM) of the periodic interrupt timer and real-time clock. The RTDIV field in
the SCCR specifies the division factor ( ÷ by 4 or ÷ by 512).
Table 5-2. Reset Clock Source Configuration
MODCK
[1:2]
POWER-ON
RESET
(POR)
DEFAULT
MF + 1
AT POR
PITRTCLK
DIVISION
DEFAULTS
AT POR
TMBCLK
DIVISION
DEFAULTS
AT POR
SPLL OPTIONS
00 0 513 4 4 Normal operation, SPLL enabled.
Main timing reference is OSCM
freq
= 32 kHz.
01 0 5 512 4 Normal operation, SPLL enabled.
Main timing reference is OSCM
freq
= 4 MHz.
11 0 5 512 4 Normal operation, SPLL enabled.
Main timing reference is EXTCLK
freq
= 4 MHz.
10 0 1 512 16 Normal operation, SPLL enabled.
One-to-one Mode, Maximum
OSCM
freq
= EXTCLK
freq
— 1 — — — The configuration remains unchanged.

Motorola MPC823e Specifications

General

Brand	Motorola
Model	MPC823e
Category	Computer Hardware
Language	English