SAB 82525
SAB 82526
SAF 82525
SAF 82526
The four selector channels of ADMA are used for serving the four DMA request sources of
HSCX, allowing very high data rates at both the system bus and the serial channels.
Another big advantage of the ADMA is it’s data chaining feature, providing an optimized
memory management for receive and transmit data. Recording the HSCX, a linked chain of 32
byte deep buffers can be set up, which are subsequently filled with the contents of the HSCX’s
FIFOs during reception. Not used buffers can be saved and linked to another buffer chain
reserved for the reception of the next frame.
As a result, it’s not necessary to reserve a very large space in system memory, determined by
the maximum frame length of every received frame.
In this example, the ADMA works directly at the CPU’s local bus and shares the same bus
interface logic (address latches, transceivers, bus controller) with the SAB 80186. Since one
DMA acknowledge line is provided for each DMA request, two DACK outputs must be ANDed
together for input to the HSCX.
The HSCX’s data lines are connected to the lower half of the system data bus (D0 … D7) and
the address lines to A1 … A7, thus (from the CPU’s point of view) all internal register
addresses must be multiplied by two (even register addresses only).
e.g. CMDR register: HSCX address 61 < = > system address C2 .
H
H
1.3 Functional Description
General
The HSCX distinguishes from other low level HDLC devices by its advanced characteristics.
The most important are:
Enlarged support of link configurations.
Beyond the point-to-point configurations, the HSCX directly enables point-to-multipoint or
multimaster configurations without additional hardware or software expense.
In point-to-multipoint configurations, the HSCX can be used as a master as well as a slave
station. Even when working as slave station, the HSCX can initiate the transmission of data at
any time. An internal function block provides means of idle and collision detection and collision
resolution, which are necessary if several stations start transmitting simultaneously.
These features were integrated to support multimaster configurations.
Semiconductor Group
21
SIEMENS [ Siemens Semiconductor Group ]
