From fff30faa4f965b1b87dfe0012532a17d7eccb436 Mon Sep 17 00:00:00 2001 From: AJR Date: Fri, 28 Sep 2018 11:23:44 -0400 Subject: dp8350: Further notes (nw) --- src/devices/video/dp8350.cpp | 16 ++++++++++------ 1 file 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; } -- cgit v1.2.3