TMS55166 datasheet(30/70 Pages) TI

30 / 70 page

TMS55165, TMS55166, TMS55175, TMS55176

262144 BY 16-BIT MULTIPORT VIDEO RAM

SMVS463 – DECEMBER 1995

POST OFFICE BOX 1443

• HOUSTON, TEXAS 77251–1443

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 is accessed from the SAM at the rising edge

of serial clock SC. SE low enables the outputs. SE high disables the outputs. Holding SE high does not disable

SC. The rising edge of SC automatically increments the internal serial-address counter regardless of the state

of SE. In full-register-transfer operations, the counter proceeds sequentially to the most significant bit (bit 255),

and then wraps around to the least significant bit (bit 0), as shown in Figure 24.

255

254

Tap

Figure 24. Serial-Pointer Direction for Serial Read

In split-register-transfer operations, serial data can be read out from the active half of 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 127 or bit 255. 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 25).

127

126

Tap

255

254

Tap

128

Figure 25. Serial Pointer for Split-Register Read – Case I

If there is no split-register transfer to the inactive half during this period, the serial pointer points to the next bit,

bit 128 or bit 0, respectively (see Figure 26).

127

126

Tap

255

254

Tap

128

Figure 26. Serial Pointer for Split-Register Read – Case II

split-register programmable stop point

The TMS551xx offers programmable stop-point mode for split-register-transfer read operation. This mode can

be used to improve 2-D drawing performance in a nonscanline data format.

In split-register-transfer read operations, 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 27).

255

128

127

Partition

Length

Stop

Points

Figure 27. Example of SAM With Partitions

TMS55166 Datasheet(PDF) 30 Page - Texas Instruments

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