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PC7447 Datasheet(PDF) 53 Page - ATMEL Corporation |
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PC7447 Datasheet(HTML) 53 Page - ATMEL Corporation |
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53 / 66 page  53 PC7457/47 [Preliminary] 5345B–HIREL–02/04 4. In PLL-off mode, no clocking occurs inside the PC7455 regardless of the SYSCLK input. The PC7457 generates the clock for the external L3 synchronous data SRAMs by divid- ing the core clock frequency of the PC7457. The core-to-L3 frequency divisor for the L3 PLL is selected through the L3_CLK bits of the L3CR register. Generally, the divisor must be chosen according to the frequency supported by the external RAMs, the fre- quency of the PC7457 core, and timing analysis of the circuit board routing. Table 19 shows various example L3 clock frequencies that can be obtained for a given set of core frequencies. Notes: 1. The core and L3 frequencies are for reference only. Note that maximum L3 frequency is design dependent. Some examples may represent core or L3 frequencies which are not useful, not supported, or not tested for the PC7457; see “L3 Clock AC Specifications” on page 24 for valid L3_CLK frequencies and for more information regarding the maximum L3 frequency. 2. These core frequencies are not supported by all speed grades; see Table 8 on page 20. Table 19. Sample Core-to-L3 Frequencies(1) Core Frequency (MHz) ÷2 ÷2.5 ÷3÷3.5÷4÷4.5÷5÷5.5÷6÷6.5÷7÷7.5÷8 500 250 200 167 143 125 111 100 91 83 77 71 67 63 533 266 213 178 152 133 118 107 97 89 82 76 71 67 550 275 220 183 157 138 122 110 100 92 85 79 73 69 600 300 240 200 171 150 133 120 109 100 92 86 80 75 650 325 260 217 186 163 144 130 118 108 100 93 87 81 666 333 266 222 190 167 148 133 121 111 102 95 89 83 700 350 280 233 200 175 156 140 127 117 108 100 93 88 733 367 293 244 209 183 163 147 133 122 113 105 98 92 800 400 320 266 230 200 178 160 145 133 123 114 107 100 866 433 347 289 248 217 192 173 157 145 133 124 115 108 933 467 373 311 266 233 207 187 170 156 144 133 124 117 1000 500 400 333 285 250 222 200 182 166 154 143 133 125 1050(2) 525 420 350 300 263 233 191 191 175 162 150 140 131 1100(2) 550 440 367 314 275 244 200 200 183 169 157 147 138 1150(2) 575 460 383 329 288 256 209 209 192 177 164 153 144 1200(2) 600 480 400 343 300 267 218 218 200 185 171 160 150 1250(2) 638 500 417 357 313 278 227 227 208 192 179 167 156 1300(2) 650 520 433 371 325 289 236 236 217 200 186 173 163 |
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