Digi RCM4000 - Manual (Page 91)

User’s Manual 85
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
29.4 MHz 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-5 lists the capacitance for the various RCM4000 I/O ports.
Table A-6 lists 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-7 lists the loadings for the A/D converter inputs.
Table A-5. Capacitance of Rabbit 4000 I/O Ports
I/O Ports
Input
Capacitance
(pF)
Output
Capacitance
(pF)
Parallel Ports A to E 12 14
Table A-6. 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
58.98 100
Table A-7. A/D Converter Inputs
Parameter Value
Input Capacitance 4–9.7 pF
Input Impedance
Common-Mode 6 M
Ω
Differential 7 M
Ω