Digi RCM4000 I/O Buffer Sourcing and Sinking Limit, Bus Loading, Table A-7. A/D Converter Inputs

A.3 I/O Buffer Sourcing and Sinking Limit

Unless otherwise specified, the Rabbit I/O buffers are capable of sourcing and sinking 8 mA of current per pin at full AC switching speed. Full AC switching assumes a

29.4MHz CPU clock with the clock doubler enabled and capacitive loading on address and data lines of less than 70 pF per pin. The absolute maximum operating voltage on all I/O is 3.6 V.

A.4 Bus Loading

You must pay careful attention to bus loading when designing an interface to the RCM4000. This section provides bus loading information for external devices.

Table A-5lists the capacitance for the various RCM4000 I/O ports.

Table A-5. Capacitance of Rabbit 4000 I/O Ports

	Input	Output
I/O Ports	Capacitance	Capacitance
	(pF)	(pF)
Parallel Ports A to E	12	14

Table A-6lists the external capacitive bus loading for the various RCM4000 output ports. Be sure to add the loads for the devices you are using in your custom system and verify that they do not exceed the values in Table A-6.

Table A-6. External Capacitive Bus Loading -40°C to +85°C

Output Port	Clock Speed	Maximum External
	(MHz)	Capacitive Loading (pF)
All I/O lines with clock	58.98	100
doubler enabled

Table A-7lists the loadings for the A/D converter inputs.

Table A-7. A/D Converter Inputs

Parameter	Value
Input Capacitance	4–9.7 pF
Input Impedance	Common-Mode 6 MΩ
	Differential 7	MΩ

User’s Manual 85