HFC-Smini Cologne Chip AG, HFC-Smini Datasheet - Page 15

• Manufacturer Part Number: HFC-Smini
• Manufacturer: Cologne Chip AG

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3.2.1.1 Send channels (B1, B2, D and PCM transmit)
The send channels send data from the host bus interface to the FIFO and the HFC-S mini converts the
data into HDLC code and tranfers it from the FIFO into the S/T or/and the PCM bus interface write
registers.
The HFC-S mini checks Z1 and Z2. If Z1=Z2 (FIFO empty) the HFC-S mini generates a HDLC-Flag
(01111110) or idle pattern (1111 1111) and sends it to the S/T device. In this case Z2 is not incremented.
If also F1=F2 only HDLC flags are sent to the S/T interface and all counters remain unchanged. If the
frame counters are unequal F2 is incremented and the HFC-S mini tries to send the next frame to the
output device. After the end of a frame (Z2 reaches Z1) it automatically generates the 16 bit CRC
checksum and adds the ending flag. If there is another frame in the FIFO (F1 F2) the F2 counter is
incremented.
With every byte being sent from the host bus side to the FIFO Z1 is incremented automatically. If a
complete frame has been sent F1 must be incremented to send the next frame. If the frame counter F1 is
incremented also the Z-counters may change because Z1 and Z2 are functions of F1 and F2. So there are
Z1(F1), Z2(F1), Z1(F2) and Z2(F2) (see Figure 3).
Z1(F1) is used for the frame which is just written from the microprocessor bus side. Z2(F2) is used for
the frame which is just beeing transmitted to the S/T device side of the HFC-S mini. Z1(F2) is the end of
frame pointer of the current output frame.
In the send channels F1 is only changed from the microprocessor interface side if the software driver
wants to say „end of send frame“. Then the current value of Z1 is stored, F1 is incremented and Z1 is
used as start address of the next frame. Z1(F2) and Z2(F2) can not be accessed.
3.2.1.2 Automatically D-channel frame repetition
The D-channel send FIFO has a special feature. If the S/T interface signals a D-channel contention
before the CRC is sent the Z2 counter is set to the starting address of the current frame and the HFC-S
mini tries to repeat the frame automatically.
*
The HFC-S mini begins to transmit the bytes from a FIFO at the moment the FIFO is changed or
the F1 counter is incremented. Also changing to the FIFO that is already selected starts the
transmission. So by selecting the same FIFO again transmission can be started. This is required if a
HDLC frame is longer than 128 bytes.
important!
Cologne
Chip