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Diffstat (limited to 'src/devices/video/dp8350.cpp')
-rw-r--r--src/devices/video/dp8350.cpp16
1 files changed, 10 insertions, 6 deletions
diff --git a/src/devices/video/dp8350.cpp b/src/devices/video/dp8350.cpp
index 74bdb7653b2..0eddc51e601 100644
--- a/src/devices/video/dp8350.cpp
+++ b/src/devices/video/dp8350.cpp
@@ -7,13 +7,17 @@
These dedicated CRTC devices are “programmable” by specifying a
long list of mask parameters. The number of parameters adjustable
through software is relatively small, there being no dedicated
- microprocessor data bus.
+ microprocessor data bus. In practice, however, the CPU's D0 and
+ D1 are usually tied to the Register Select lines, due to shared
+ use of the address bus for DMA purposes.
National released the DP8350 and a few other standard versions.
DP8367 appears to have originally been a custom mask variant
ordered by Hewlett-Packard, though it is listed as option “I” in
later datasheets; its parameters have been derived from the
- information presented in Manual Part No. 13220-91087.
+ information presented in Manual Part No. 13220-91087. (The 8367
+ designation also comes from there, since the actual IC is merely
+ marked with its HP part number, 1820-2373.)
Variant Dot rate Monitor type
------- -------- ------------
@@ -292,21 +296,21 @@ void dp835x_device::register_load(u8 rs, u16 addr)
{
case 0:
default:
- // No Select
+ // A = 0, B = 0: No Select
break;
case 1:
- // Top-of-Page
+ // A = 0, B = 1: Top-of-Page
logerror("Top-of-Page Register = %03X\n", addr);
break;
case 2:
- // Row Start
+ // A = 1, B = 0: Row Start (also Top-of-Page during vertical blanking)
logerror("Row Start Register = %03X\n", addr);
break;
case 3:
- // Cursor
+ // A = 1, B = 1: Cursor
logerror("Cursor Register = %03X\n", addr);
break;
}