Symmetricom, Inc.
bc620/627AT Time and Frequency Processor
4-1
CHAPTER FOUR
FIFO DATA PACKETS
4.0 GENERAL
Communication with the bc620/627AT Time and Frequency Processor (TFP) is performed using
byte serial data packet protocol. The packet bytes are read from and written to the TFP using
eight bit data transfers at offset 0x0E of PAGE1. Following is a description of the available
TFP FIFO data packets and the programming protocol.
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 zero of the ACK register by writing 0x01 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 zero of the ACK register when the packet is processed.
When the host sets bit 7 of the ACK register and an interrupt is generated to the TFP CPU, the
TFP service routine performs minimalist packet integrity checking. The TFP checks that the
first packet byte is 0x01 (ASCII SOH). If the SOH is found, the TFP loads FIFO data into an
input buffer until a byte value of 0x17 (ASCII ETB) is found. The packet is then processed in
accordance with the idbyte value. When processing is complete the TFP sets bit 1 of the ACK
register, clears the input FIFO, and resumes its previous task. If 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 of the ACK register, and resumes its previous task.
A demonstration program written in the “C” language is provided with the disk accompanying
the TFP. This program demonstrates the use of the primary data packets described below.
4.1.1 PACKET “A” - SELECT OPERATIONAL MODE
This packet contains a single data byte defining the operational mode of the TFP. Five
operational modes are supported, modes 0, 1, 2, 3, and 4 corresponding to ASCII data bytes “0,”
“1,” ... “4.”
Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com
