HSP3824
The second transmit scenario supported by the HSP3824 is
TX Port
when the preamble and header information are provided by
the external data source. During this mode TX_RDY is not
required as part of the TX handshake. The HSP3824 will
immediately start transmitting the data available on TXD
upon assertion of TX_PE. The timing diagram of this TX sce-
nario, where the preamble and header are generated exter-
nal to the HSP3824, is illustrated on Figure 5.
The transmit data port accepts the data that needs to be
transmitted serially from an external data source. The data is
modulated and transmitted as soon as it is received from the
external data source. The serial data is input to the
HSP3824 through TXD using the falling edge of TXCLK to
clock it in the HSP3824. TXCLK is an output from the
HSP3824. A timing scenario of the transmit signal hand-
shakes and sequence is shown on timing diagram Figures 5
and 6.
One other signal that can be used for certain applications as
part of the TX interface is the Clear Channel Assessment
(CCA) signal which is an output from the HSP3824. The
CCA is programmable and it is described with more detail in
the Transmitter section of this document. CCA provides the
indication that the channel is clear of energy and the trans-
mission will not be subject to collisions. CCA can be moni-
tored by the external processor to assist in deciding when to
initiate transmissions. The CCA indication can bypassed or
ignored by the external processor. The state of the CCA
does not effect the transmit operation of the HSP3824.
TX_PE alone will always initiate the transmit state indepen-
dent of the state of CCA. Signals TX_RDY, TX_PE and
TXCLK can be set individually, by programming Configura-
tion Register (CR) 9, as either active high or active low sig-
nals.
The external processor initiates the transmit sequence by
asserting TX_PE. TX_PE envelopes the transmit data
packet on TXD. The HSP3824 responds by generating
TXCLK to input the serial data on TXD. TXCLK will run until
TX_PE goes back to its inactive state indicating the end of
the data packet. There are two possible transmit scenarios.
One scenario is when the HSP3824 internally generates the
preamble and header information. During this mode the
external source needs to provide only the data portion of the
packet. The timing diagram of this mode is illustrated on Fig-
ure 6. When the HSP3824 generates the preamble inter-
nally, assertion of TX_PE will initialize the generation of the
preamble and header. TX_RDY, which is an output from the
HSP3824, is used to indicate to the external processor that
the preamble has been generated and the device is ready to
receive the data packet to be transmitted from the external
processor. The TX_RDY timing is programmable in case the
external processor needs several clocks of advanced notice
before actual data transmission is to begin.
The transmit port is completely independent from the opera-
tion of the other interface ports including the RX port, there-
fore supporting a full duplex mode.
TXCLK
TX_PE
TXD
LSB
DATA PACKET
MSB
DUMMY BITS TO CLEAR MOD PATH
PREAMBLE - HEADER
MSB OF LAST HEADER FIELD
NOTE: Preamble/Header and Data is transmitted LSB first TX_RDY is inactive Logic 0 when generated externally. TXD shown generated
from rising edge TXCLK.
FIGURE 5. TX PORT TIMING (EXTERNAL PREAMBLE)
TXCLK
TX_PE
TXD
PREAMBLE - HEADER
LSB
DATA PACKET
MSB
DUMMY BITS TO CLEAR MOD PATH
MSB OF LAST HEADER FIELD
TX_RDY
NOTE: Preamble/Header and Data is transmitted LSB first. TXD shown generated from rising edge TXCLK. TX_RDY generated from falling edge.
FIGURE 6. TX PORT TIMING (INTERNAL PREAMBLE)
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HARRIS [ HARRIS CORPORATION ]
