TMS55165 Datasheet, PDF (16/70 Pages) Texas Instruments – 262144 BY 16-BIT MULTIPORT VIDEO RAM

TMS55165, TMS55166, TMS55175, TMS55176
262144 BY 16-BIT MULTIPORT VIDEO RAM
SMVS463 – DECEMBER 1995
nonpersistent write-per-bit
When either or both WEL and WEU are low on the falling edge of RAS, the write mask is reloaded. A 16-bit binary
code (the write mask) is input to the device via the DQ pins and latched on the falling edge of RAS. The
write-per-bit mask selects which of the 16 DQs are to be written and which are not. After RAS has latched the
on-chip write-per-bit mask, input data is driven onto the DQ pins and is latched on either the falling edge of CAS
or the first falling edge of WEx, whichever occurs later. WEL enables the lower byte (DQ0 – DQ7) to be written
through the mask and WEU enables the upper byte (DQ8 – DQ15) to be written through the mask. If a write mask
low (write mask = 0) is latched into a particular DQ pin on the falling edge of RAS, write data is not written to
that DQ. If a write mask high (write mask = 1) is latched into a particular DQ pin on the falling edge of RAS, write
data is written to that DQ (see Figure 6).
RAS
CAS
WEL
WEU
tsu(DQR)^†
th(RDQ)^†
tsu(DWL)^†
th(WLD)^†
DQ0 – DQ15
Write Mask
Write Data
† _{See “timing requirements over recommended ranges of supply voltage and operating free-air temperature” table.}
Figure 6. Example of a Nonpersistent Write-Per-Bit (Late-Write) Operation
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