MC68336/376
ELECTRICAL CHARACTERISTICS
MOTOROLA
USER’S MANUAL
Rev. 15 Oct 2000
A-3
Table A-4 Clock Control Timing
(VDD and VDDSYN = 5.0 Vdc ± 5%, VSS = 0 Vdc, TA = TL to TH, 4.194 MHz reference)
Num
Characteristic
Symbol
Min
Max
Unit
1
PLL Reference Frequency Range
fref
4.194
5.243
MHz
2
System Frequency1
On-Chip PLL System Frequency
External Clock Operation
NOTES:
1. All internal registers retain data at 0 Hz.
fsys
dc
fref/32
dc
20.97
MHz
3
PLL Lock Time2, 3, 4, 5
2. This parameter is periodically sampled rather than 100% tested.
3. Assumes that a low-leakage external filter network is used to condition clock synthesizer input voltage. Total
external resistance from the XFC pin due to external leakage must be greater than 15 M
to guarantee this
specification. Filter network geometry can vary depending upon operating environment
.
4. Proper layout procedures must be followed to achieve specifications.
5. Assumes that stable VDDSYN is applied, and that the crystal oscillator is stable. Lock time is measured from the
time VDD and VDDSYN are valid until RESET is released. This specification also applies to the period required
for PLL lock after changing the W and Y frequency control bits in the synthesizer control register (SYNCR) while
the PLL is running, and to the period required for the clock to lock after LPSTOP.
tlpll
—20
ms
4
VCO Frequency6
6. Internal VCO frequency (fVCO ) is determined by SYNCR W and Y bit values. The SYNCR X bit controls a di-
vide-by-two circuit that is not in the synthesizer feedback loop. When X = 0, the divider is enabled, and fsys =
fVCO ÷ 4. When X = 1, the divider is disabled, and fsys = fVCO ÷ 2. X must equal one when operating at maximum
specified fsys.
fVCO
—2 (fsys max)
MHz
5
Limp Mode Clock Frequency
SYNCR X bit = 0
SYNCR X bit = 1
flimp
—
fsys max/2
fsys max
MHz
6
Short term (5
s interval)
Long term (500
s interval)
7. Jitter is the average deviation from the programmed frequency measured over the specified interval at maxi-
mum fsys. Measurements are made with the device powered by filtered supplies and clocked by a stable exter-
nal clock signal. Noise injected into the PLL circuitry via VDDSYN and VSS and variation in crystal oscillator
frequency increase the Jclk percentage for a given interval. When jitter is a critical constraint on control system
operation, this parameter should be measured during functional testing of the final system.
J
clk
–0.625
–0.0625
–0.625
–0.0625
%