CHAPTER 4
FIFO DATA PACKETS
4.0 GENERAL
Communication with the TFP is performed using a byte serial data packet protocol. The packet bytes
are read from and written to the TFP using D08(0) transfers at offset 0x27 or D16 transfers at offset
0x26. I f the case of a D16 transfer only the low order byte is used. The packet structure is defined
in CHAPTER 3 Section 3.1 OFFSET 0x26.
4.1 WRITING DATA PACKETS
The following steps should be followed when loading data packets to the TFP. Failure to perform
one or more of these steps correctly is a common reason for customer support calls.
Write the packet to the input
FIFO.
Clear bit 0 of the
ACK
register by writing Ox01 to the
ACK
register.
Inform the TFP that an input packet is available by writing 0x80 to the
ACK
register.
The TFP will set bit 0 of the
ACK
register when the packet is processed.
When the host sets bits 7 of the
ACK
register an interrupt to the TFP CPU is generated. The TFP
service routine performs minimalist packet integrity checking. The TFP checks that the first packet
byte is Ox01 (ASCII SOH). I f the SOH is found the TFP loads
FIFO
data into an input buffer until
a byte value of Ox17 (ASCII ETB) is found. The packet is then processed in accordance with the
idbyte value. When processing is complete the TFP sets bit 1 o f the
ACK
register, clears the input
FIFO,
and resumes its previous task. I f an SOH is not the first packet byte or if more than 40 bytes
are read before encountering an ETB or if the idbyte value is invalid, then TFP clears the
FIFO,
sets
bits 1 o f the
ACK
register, and resumes its previous task.
4.1.1 PACKET 'A' - SELECT TFP OPERATIONAL MODE
This packet contains a single data byte ('0' through '7') which defines the TFP operational mode. The
modes are enumerated below.
MODE 0 T I M E C O D E DECODING MODE
The TFP uses an input timecode as the timing reference. The following codes are supported (see
packet 'H'): IRIGA, IRIGB, 2137, XR3, and NASA36. Both modulated carrier and DC level shift
formats are supported (DC level shift is not supported for 2137 or XR3 codes). The TFP locks its
crystal oscillator to the input code rate. The oscillator has a control range of +/- 30 PPM for the
standard DIP version, and +/- 2 PPM for the optional oven version. I f the input code is outside these
limits the TFP will exhibit periodic slips (if the TFP reference deviates from the input source by
more than +/- 1 millisecond a forced jamsync is performed). I f the input code is lost or removed
theTFP will continue to 'flywheel' at the last known code rate. Typical accuracy is 5 parts in 10E7
Datum Inc., Bancomm Div.
bc635VME/bc350VXI Manual
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