SM55161A Datasheet, PDF (22/64 Pages) Austin Semiconductor – 262144 x 16 BIT VRAM MULTIPORT VIDEO RAM

Austin Semiconductor, Inc.
VRAM
SM55161A
Production
serial-read operation
The serial-read operation can be performed through the
SAM port simultaneously and asynchronously with DRAM
operations except during transfer operations. Serial data can be
read from the SAM by clocking SC starting at the tap point
loaded by the preceding transfer cycle, proceeding
sequentially to the most significant bit (bit 255), and then
wrapping around to the least significant bit (bit 0), as shown in
Figure 19.
For split-register-transfer-read operation, serial data can
be read out from the active half of the SAM by clocking SC
starting at the tap point loaded by the preceding split-
register-transfer cycle. The serial pointer then proceeds
sequentially to the most significant bit of the half, bit 255 or bit
511. If there is a split-register-transfer read to the inactive half
during this period, the serial pointer points next to the tap point
location loaded by that split-register transfer (see Figure 20).
If there is no split-register-transfer read to the inactive half
during this period, the serial pointer points next to bit 256 or bit
0, respectively (see Figure 21).
split-register programmable stop point
The SMJ55161A offers a programmable stop-point mode
for split-register-transfer read operations. This mode can be
used to improve two-dimensional drawing performance in a
nonscanline data format.
For a split-register-transfer-read operation, the stop point
is defined as a register location at which the serial output stops
coming from one half of the SAM and switches to the opposite
half of the SAM. While in stop-point mode, the SAM is divided
into partitions whose length is programmed via row addresses
A4–A7 in a CBR set (CBRS) cycle. The last serial-address
location of each partition is the stop point (see Figure 22).
SMJ55161A
Rev. 1.6 03/05
22
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