
PSB 7280
Semiconductor Group
60
Data Sheet 1998-07-01
Figure 24
Caption to the Figure
The data from the HDLC transmitter is loaded into DSP accessible transmit read
registers (HXR1/2) and simultaneously into (physically separate) host accessible read
registers. Data is loaded into the shift register from the transmit write register (HXW1/2)
accessible from the DSP (if HHX = 0) or the register accessible from the host
(if HHX = 1). Two separate control bits HHX1 and HHX2 are provided for this purpose,
for HDLC channel 1 and channel 2, respectively.
The access right to the receiver and transmitter write registers (HRW1/2, HXW1/2) from
the DSP or the host (determined bits HHR1,2 and HHX1,2) is independent of who is
allowed to service the HDLC controller (determined by bits HAH1,2).
Note on Time-Slots of HDLC/Transparent Data Communication Controllers
If a time-slot is still active (either in receive or transmit direction) when a new frame sync
pulse is detected, the programmed length of the time-slot is not reduced but the time-slot
remains active until its end. However, the time-slot count logic for the new frame starts
immediately at the detection of the new frame sync pulse. A new time-slot can start
immediately after the currently active time-slot has been closed, thus permitting a
permanent reception or transmission (“time-slot length” = “distance between two
consecutive frame sync's”).
The case where “time-slot length” > “distance between two consecutive frame sync's”
should not occur.