User`s manual

User’s Manual 63
A.2 Bus Loading
You must pay careful attention to bus loading when designing an interface to the
RCM3400. This section provides bus loading information for external devices.
Table A-2 lists the capacitance for the various RCM3400 I/O ports.
Table A-3 lists the external capacitive bus loading for the various RCM3400 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-3.
Table A-4 lists the loadings for the A/D converter inputs.
Table A-2. Capacitance of Rabbit 3000 I/O Ports
I/O Ports
Input
Capacitance
(pF)
Output
Capacitance
(pF)
Parallel Ports A to G 12 14
Table A-3. External Capacitive Bus Loading -40°C to +85°C
Output Port
Clock Speed
(MHz)
Maximum External
Capacitive Loading (pF)
All I/O lines with clock
doubler enabled
29.4 70
All I/O lines with clock
doubler disabled
14.7456 100
Table A-4. A/D Converter Inputs
Parameter Value
Input Capacitance 4–9.7 pF
Input Impedance
Common-Mode 6 M
Differential 7 M