64 Rabbit 2000 Microprocessor5.7 I/O Buffer Sourcing and Sinking LimitUnless otherwise specified, the Rabbit I/O buffers are capable of sourcing and sinking 8 mAof current per pin at full AC switching speed. Full AC switching assumes 22.11 MHz CPUclock and capacitive loading on address and data lines of less than 100 pF per pin. Addresspin A0 and Data pin D0 are rated at 16 mA each.Table 5-6 shows the AC and DC output drive limits of the parallel I/O buffers.Table 5-6. I/O Buffer Sourcing and Sinking CapabilityPin NameOutput DriveSourcing*/Sinking † Limits(mA)* The maximum DC sourcing current for I/O buffers between VDD pinsis 112 mA.† The maximum DC sinking current for I/O buffers between VSS pins is150 mA.Output Port Name Full AC SwitchingSRC/SNKMaximum ‡ DC OutputDriveSRC/SNK‡ The maximum DC output drive on I/O buffers must be adjusted to takeinto consideration the current demands made my AC switching out-puts, capacitive loading on switching outputs, and switching voltage.The current ascribed to AC switching is the average current that flowswhile AC switching is taking place. This can be computed using I =CVf, where f is the number of transitions per second, C is the capaci-tance switched, and V is the voltage swing. For example, if 12,000,000transitions per second take place with a 5 V swing driving 100 pF, thenI = 6 mA for one pin. The current attributable to all the pins betweenthe power or ground pins must be summed to test the limits, includingthe current attributable to switching current or DC current.The current drawn by all switching and non-switching I/O must notexceed the limits specified in the first two footnotes.PA [7:0] 8/8 12/12PB [7:6] 8/8 12/12PC [6, 4, 2, 0] 8/8 12/12PD [7:4] 8/8 12/12PD [3:0]****The combined sourcing from Port D [7:0] may need to be adjusted soas not to exceed the 112 mA sourcing limit requirement specifiedabove.16/16 25/25PE [7:0] 8/8 12/12
