
PSB 7280
Semiconductor Group
63
Data Sheet 1998-07-01
4.3
HDLC Controller
The two internal HDLC controllers of the PSB 7280 can be independently serviced
– either via the Parallel Host Interface
– or by the DSP (SPCF).
Important Notes
1. From the point of view of the end user/system manufacturer, only the servicing of the
HDLC controllers via the host is of relevance, since the servicing via the DSP is done
by on-chip firmware invisible to the end user.
2. If the packet oriented protocol on the Serial Audio Interface used in videophone
applications with the VCP (from 8
×
8, Inc.) videocodec is needed, the HDLC1
controller is serviced by the on-chip firmware, in other words, it cannot be accessed
by the host: only HDLC2 controller will then be available to the user.
The servicing of the HDLC controller(s) via the host and via the embedded DSP are
exclusive of each other. The access to the register banks of the two HDLC controllers is
determined by the “HDLC Controller Access from Host” bits HAH1 (for HDLC1) and
HAH2 (for HDLC2):
– When HAHx is ‘0’, the SPCF is allowed to access the HDLC register bank, and the
host interface bus is disconnected from the HDLC controller;
– When HAHx is ‘1’, the host is allowed to access the HDLC register bank, and the
SPCF data bus is disconnected from the HDLC controller.
The address spaces of the two HDLC controllers for the host interface bus and for the
SPCF data bus is shown in
Figure 25
(see also
Chapter 5
):
Figure 25