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hardware:screen_map [2016/06/05 15:15] ex_writer |
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In the Bally Arcade, two bits of RAM define each screen pixel. Therefore, one 8-bit byte of RAM defines four pixels on the screen. | In the Bally Arcade, two bits of RAM define each screen pixel. Therefore, one 8-bit byte of RAM defines four pixels on the screen. | ||
- | In low-resolution mode, 40 bytes define a line of screen data, providing a horizontal resolution of 160 pixels. The vertical resolution is 102 lines. The areas of the screen defined by the display RAM therefore requires 102 x 40 = 4,080 bytes. The remaining 16 bytes of screen RAM are used for [[:glossary#s|scratchpad]]. More RAM can be reserved for scratchpad by [[hardware:interrupts#vertical blank|blanking]] the screen before the 102nd line. | + | In low-resolution (aka "consumer") mode, 40 bytes define a line of screen data, providing a horizontal resolution of 160 pixels. The vertical resolution is 102 lines. The areas of the screen defined by the display RAM therefore requires 102 x 40 = 4,080 bytes. The remaining 16 bytes of screen RAM are used for [[:glossary#s|scratchpad]]. More RAM can be reserved for scratchpad by [[hardware:interrupts#vertical blank|blanking]] the screen before the 102nd line. |
The first byte of RAM is in the upper lefthand corner of the screen. As RAM addresses increases, the screen position moves in the same direction as the TV scan: from left to right and from top to bottom. The four pixels in each byte are displayed with the least significant pixel (bits 0 and 1) on the right. | The first byte of RAM is in the upper lefthand corner of the screen. As RAM addresses increases, the screen position moves in the same direction as the TV scan: from left to right and from top to bottom. The four pixels in each byte are displayed with the least significant pixel (bits 0 and 1) on the right. | ||
{{:screen_map.png}} | {{:screen_map.png}} | ||
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+ | In consumer mode, each line is scanned twice per field (the second time immediately after the first), to give 204 active lines of video. The remaining 58 1⁄2 lines of video (each NTSC field is 262 1⁄2 lines) is made up of blanking and sync lines. Each frame consists of two fields, scanned in an interlaced format, at 60 fields (or 30 frames) per second. | ||
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[NM:85–6] | [NM:85–6] | ||
+ | **Reference:** Tony Miller, [[http://www.ballyalley.com/faqs/BPA%20Video%20Hardware%20FAQ/Bally_Professional_Arcade_Video_Hardware%20(2001)(Tony%20Miller).pdf|A Description of the Bally Professional Arcade Video Hardware and Associated Coin-Operated Hardware]] (2001) |