| Revision | 6337fc61df7b423d32bd1abcec9fb62bbdfd9d31 (tree) |
|---|---|
| Time | 2019-01-14 20:41:21 |
| Author | inglorion <homemicro@ingl...> |
| Commiter | inglorion |
faster memory map using a single AC part
docs/design/memory-map.txt (diff)| @@ -263,6 +263,7 @@ | ||
| 263 | 263 | - 74HC08 has 23ns propagation delay at 85C. |
| 264 | 264 | - 74AC08 has 8.5ns propagation delay at 85C. |
| 265 | 265 | - 74HC10 has 24ns propagation delay at 85C. |
| 266 | + - 74AC10 has 8ns propagation delay at 85C. | |
| 266 | 267 | - 74HC11 has 25ns propagation delay at 85C. |
| 267 | 268 | - 74HC32 has 23ns propagation delay at 85C. |
| 268 | 269 | - 74AC32 has 8.5ns propagation delay at 85C. |
| @@ -289,7 +290,10 @@ | ||
| 289 | 290 | |
| 290 | 291 | Alternatively, could us an AC245 instead of an HC245. 10.5ns instead |
| 291 | 292 | of 38ns. Increases budget from 31ns to 58ns. But CPU still needs 25ns, |
| 292 | -so more like 31ns to 44ns. | |
| 293 | +so more like 31ns to 44ns. Could use AC245 (or 241) to control the | |
| 294 | +CPU's bus access, which would give the 10.5ns at the expense of needing | |
| 295 | +additional ICs. It would also allow using CPUs without the bus enable | |
| 296 | +line. This also works with ACT241, which would take about 11ns. | |
| 293 | 297 | |
| 294 | 298 | Faster: |
| 295 | 299 |
| @@ -308,5 +312,19 @@ | ||
| 308 | 312 | : |
| 309 | 313 | : ram# = and hi hiram# (23 + 48 = 71) |
| 310 | 314 | |
| 315 | +Another possibility, which avoids the or gate: | |
| 316 | + | |
| 317 | + : rom#: nand a15 a14 a13 (24) | |
| 318 | + : hi_odd#: nand a15 a14 a12 (24) | |
| 319 | + : | |
| 320 | + : ram#: nand rom# hi_odd# (24 + 24 = 48) | |
| 321 | + | |
| 322 | +This all works with a single '10, so we can make it all faster by going with an AC10: | |
| 323 | + | |
| 324 | + : rom#: nand a15 a14 a13 (8) | |
| 325 | + : hi_odd#: nand a15 a14 a12 (8) | |
| 326 | + : | |
| 327 | + : ram#: nand rom# hi_odd# (8 + 8 = 16) | |
| 328 | + | |
| 311 | 329 | * COMMENT Customization for HTML export. |
| 312 | 330 | #+HTML_HEAD: <link rel="stylesheet" type="text/css" href="../style.css" /> |
Fork