Sonic Alert msm85c154hvs, msm83c154s, msm80154s user manual INPUT/OUTPUT Ports

INPUT/OUTPUT PORTS

5.6Port 0, 1, 2, and 3 Output and Floating Status Settings in CPU Power Down Mode (PD, HPD)

The port 0, 1, 2, and 3 output status can be set to either data output or floating when MSM80C154S/MSM83C154S is in power down mode (PD, HPD).

To set these ports to output status in power down mode, bit 0 (ALF) of the I/O control register (IOCON 0F8H) is reset to “0” before PD or HPD mode is activated (see Figure 5-11). The CPU is then stopped with the ports in data output status when power down mode is started.

And to set the ports to floating status in power down mode, “1” is set in bit 0 (ALF) of the I/ O control register (IOCON 0F8H) before PD or HPD mode is activated (see Figure 5-11). The port output driver is disconnected from the port pins when power down mode is started.

If “1” output from port becomes a power supply factor in respect to the external circuits when PD or HPD mode is activated in port data output mode, the PD or HPD mode should be activated after the port data is reset to “0” by software. And in the reverse case, PD or HPD mode is activated after the port data is set to “1”.

When port pins are in floating status during PD or HPD mode, the port pin status of all pins except pins 2 thru 5 of port 3 may be either open or undefined in the –0.5 to VCC+0.5V range. This mode is used only in battery back-up of CPU data.

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