ADSP-BF537 Blackfin Processor Hardware Reference
13-9
UART Port Controllers
IrDA Receive Operation
The IrDA receiver function is more complex than the transmit function.
The receiver must discriminate the IrDA pulse and reject noise. To do
this, the receiver looks for the IrDA pulse in a narrow window centered
around the middle of the expected pulse.
Glitch filtering is accomplished by counting 16 system clocks from the
time an initial pulse is seen. If the pulse is absent when the counter
expires, it is considered a glitch. Otherwise, it is interpreted as a 0. This is
acceptable because glitches originating from on-chip capacitive cross-cou-
pling typically do not last for more than a fraction of the system clock
period. Sources outside of the chip and not part of the transmitter can be
avoided by appropriate shielding. The only other source of a glitch is the
transmitter itself. The processor relies on the transmitter to perform
within specification. If the transmitter violates the specification, unpre-
dictable results may occur. The 4-bit counter adds an extra level of
protection at a minimal cost. Note because the system clock can change
across systems, the longest glitch tolerated is inversely proportional to the
system clock frequency.
The receive sampling window is determined by a counter that is clocked at
the 16x bit-time sample clock. The sampling window is re-synchronized
with each start bit by centering the sampling window around the start bit.
The polarity of receive data is selectable, using the
IRPOL
gives examples of each polarity type.
•
IRPOL
= 0 assumes that the receive data input idles 0 and each
active 1 transition corresponds to a UART NRZ value of 0.
•
IRPOL
= 1 assumes that the receive data input idles 1 and each
active 0 transition corresponds to a UART NRZ value of 0.
Summary of Contents for Blackfin ADSP-BF537
Page 42: ...Contents xlii ADSP BF537 Blackfin Processor Hardware Reference ...
Page 90: ...Development Tools 1 32 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 138: ...Programming Examples 4 26 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 340: ...SDC Programming Examples 6 84 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 606: ...Programming Examples 9 94 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 660: ...Programming Examples 10 54 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 720: ...Electrical Specifications 11 60 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 840: ...Programming Examples 13 42 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 876: ...Programming Examples 14 36 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 938: ...Programming Examples 15 62 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 958: ...Programming Examples 17 12 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 986: ...Programming Examples 18 28 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 1162: ...G 26 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 1218: ...Index I 56 ADSP BF537 Blackfin Processor Hardware Reference ...