
16: EPSON INDEPENDENT SIMULTANEOUS DISPLAY (EISD)
S1D13806 SERIES HARDWARE FUNCTIONAL
EPSON
1-167
SPECIFICATION (X28B-A-001-03)
16.3 Bandwidth Limitation
When EISD is enabled, the LCD and CRT/TV displays must share the total bandwidth available to
the S1D13806. The result is that display modes with a high resolution or color depth may not be
supported. In some cases, Ink Layers may not be possible on one or both of the displays. EISD
increases the total demand for display refresh bandwidth and reduces CPU bandwidth, resulting in
lower CPU performance.
In a few cases when EISD is enabled, the default LCD and CRT/TV Display FIFO High Threshold
Control register values are not optimally set, causing display problems with one or both of the dis-
plays. This condition may be corrected by adjusting the values of the LCD and CRT/TV Display
FIFO High Threshold Control registers (REG[04Ah] for LCD and REG[06Ah] for CRT/TV). See
Changing this register to a non-zero value sets the high threshold FIFO level to this value. This reg-
ister may not exceed 59 decimal. The high threshold FIFO level controls how often display fetch
requests are issued by the FIFO. In general, a higher high threshold FIFO level increases the band-
width to that display pipe, and a lower level reduces it.
When the FIFO High Threshold Control register is set to 00h (default), the following settings are
used:
11h for 4 bpp color depth
21h for 8 bpp color depth
23h for 16 bpp color depth
Most display problems may be corrected by increasing the associated high threshold FIFO level for
that display. However, because the total available bandwidth is fixed, this change may create display
problem for the other display. In this case, reducing the high threshold FIFO level for the other dis-
play instead may work. Sometimes, a combination of these two methods is required. Correcting
EISD display problems by adjusting the FIFO High Threshold Control registers is mostly a trial-
and-error process.
Note: While the user is free to experiment with these registers, recommended FIFO level settings for some
of the more common EISD modes requiring non-default FIFO level settings are listed in
Section 18.2,