C8051F340/1/2/3/4/5/6/7

23.2. C2 Pin Sharing

The C2 protocol allows the C2 pins to be shared with user functions so that in-system debugging and Flash programming functions may be performed. This is possible because C2 communication is typically performed when the device is in the halt state, where all on-chip peripherals and user software are stalled. In this halted state, the C2 interface can safely ‘borrow’ the C2CK (/RST) and C2D (P3.0) pins. In most applications, external resistors are required to isolate C2 interface traffic from the user application. A typi- cal isolation configuration is shown in Figure 23.1.

/Reset (a)

Input (b)

Output (c)

C8051Fxxx

C2CK

C2D

C2 Interface Master

Figure 23.1. Typical C2 Pin Sharing

The configuration in Figure 23.1 assumes the following:

1.The user input (b) cannot change state while the target device is halted.

2.The /RST pin on the target device is used as an input only.

Additional resistors may be necessary depending on the specific application.

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Silicon Laboratories C8051F346, C8051F347, C8051F341, C8051F343, C8051F340 23.2. C2 Pin Sharing, Typical C2 Pin Sharing