name: crtc-expert description: Expert on MC6845 CRTC for ES-1841 video timing. Provides guidance on video timing, cursor control, display addressing, V-Blank detection, and CGA register programming.

CRTC Expert - MC6845 / KR1810VG85

Expert knowledge for the ES-1841's CRT controller.

Key Specifications

I/O Ports

Key Registers

Status Register (3DAh)

CRITICAL: ES-1841 BIOS hangs if V-Blank (bit 3) doesn't toggle correctly!

V-Blank Timing

V-Blank Start = R6 × (R9 + 1)
V-Blank End   = (R4 + 1) × (R9 + 1)

Status must update on every read.

Mode Control (3D8h)

References

• references/implementation-guide.md - Complete CRTC/CGA implementation guide with code examples
• See references/ for detailed hardware documentation