|0xE000-0xE7FF||CPU RAM (B8)|
|0xF000-0xF7FF||Video RAM (F3)|
Z80 Port Map
|0xF0||In||Control panel input. Only lower 6 data bits are used. Active low.
|0xF1||In||Control panel input. Only lower 6 data bits are used. Active low.
|0xF2||In||Control panel input. Only lower 6 data bits are used.|
|0xF3||In||Control panel input. Only lower 6 data bits are used.|
|0xF4||In/Out||LD-V1000 data. Writing queues a command to be sent on the next command strobe. Reading reads the most recent byte received during last the status strobe.|
|0xF8||Out||0 disables start button lamp. 1 enables.|
|0xF9||Out||Drives EDGE_06 (on the edge connector), but we don't know what this is connected to.|
|0xFA||Out||0 disables action button lamp. 1 enables.|
|0xFB||Out||0 disables joystick lamp. 1 enables.|
|0xFE||Out||0 holds IRQ' line high (disabled) by forcing a latch to be clear. 1 stops forcing latch to be clear, which allows IRQs to set the latch.|
|0xFF||Out||0 holds NMI' line high (disabled) by forcing a latch to be clear. 1 stops forcing latch to be clear, which allows NMIs to set the latch.|
NMI: Caused by LD-V1000 status strobe going low (becoming active)
IRQ: Caused by D2 output (pin 10) on vertical PROM (C6) transitioning from 0 to 1. This ends up being 60 Hz (vsync).
Video RAM Structure
Screen is divided into 32x32 tiles. The first tile is the top left.
0xF000-0xF3FF contain which tile to show.
0xF400-0xF7FF contain tile attributes. For example, 0xF400 would have attributes about the tile index at 0xF000.
H and V PROMs are MB7052. MB7052 are compatible with 82s129 proms. One option is http://callanbrown.com/index.php/flep-prom-replacement-adapters
RGB PROM is MB7124. MB7124 are compatible with 82s147 proms. Haven't found replacement yet.
Newer EEPROMs may be fast enough. W27C512 may be a commonly available EEPROM.