Conditioning Input Signals
15-14
ADSP-2126x SHARC Processor Hardware Reference
counts up to 4096
CLKIN
cycles after
RESET
is transitioned from low to
high. The delay circuit is activated at the same time the PLL is taken out
of reset.
The advantage of the delayed core reset is that the PLL can be reset any
number of times without having to power-down the system. If there is a
brown-out situation, the watchdog circuit only has to control the
RESET
.
Conditioning Input Signals
The processor is a CMOS device. It has input conditioning circuits which
simplify system design by filtering or latching input signals to reduce sus-
ceptibility to glitches or reflections.
The following sections describe why these circuits are needed and their
effect on input signals.
A typical CMOS input consists of an inverter with specific N and P device
sizes that cause a switching point of approximately 1.4 V. This level is
selected to be the midpoint of the standard TTL interface specification of
V
IL
= 0.8 V and V
IH
= 2.0 V. This input inverter, unfortunately, has a fast
response to input signals and external glitches wider than 1 ns. Filter cir-
cuits and hysteresis are added after the input inverter on some processor
inputs, as described in the following sections.
Input Pin Hysteresis
Hysteresis (shown in
) is used on all SHARC input signals.
Hysteresis causes the switching point of the input inverter to be slightly
above 1.4 V (VT) for a rising edge (VT+) and slightly below 1.4 V for a
falling edge (VT–). The value of the hysteresis is approximately ± 100 mV.
The hysteresis is intended to prevent multiple triggering of signals that are
allowed to rise slowly, as might be expected for example on a reset line
with a delay implemented by an RC input circuit. Hysteresis is not used to
Summary of Contents for ADSP-21261 SHARC
Page 30: ...Contents xxx ADSP 2126x SHARC Processor Hardware Reference ...
Page 40: ...Register Diagram Conventions xl ADSP 2126x SHARC Processor Hardware Reference ...
Page 58: ...Differences From Previous SHARCs 1 18 ADSP 2126x SHARC Processor Hardware Reference ...
Page 112: ...Secondary Processing Element PEy 2 54 ADSP 2126x SHARC Processor Hardware Reference ...
Page 178: ...Summary 3 66 ADSP 2126x SHARC Processor Hardware Reference ...
Page 204: ...DAG Instruction Summary 4 26 ADSP 2126x SHARC Processor Hardware Reference ...
Page 322: ...Setting Up DMA 7 32 ADSP 2126x SHARC Processor Hardware Reference ...
Page 436: ...SPORT Programming Examples 9 86 ADSP 2126x SHARC Processor Hardware Reference ...
Page 521: ...ADSP 2126x SHARC Processor Hardware Reference 11 31 Input Data Port rts IDP_ISR end ...
Page 522: ...Input Data Port Programming Example 11 32 ADSP 2126x SHARC Processor Hardware Reference ...
Page 590: ...Timer Programming Examples 14 20 ADSP 2126x SHARC Processor Hardware Reference ...
Page 796: ...I O Processor Registers A 174 ADSP 2126x SHARC Processor Hardware Reference ...
Page 800: ...B 4 ADSP 2126x SHARC Processor Core Manual ...
Page 846: ...Index I 36 ADSP 2126x SHARC Processor Hardware Reference ...