Intel SA-1100 manual Peripheral Pin Controller PPC, PPC Operation, 11-184

Peripheral Control Module

11.13Peripheral Pin Controller (PPC)

The peripheral pin controller (PPC) takes individual control of the LCD’s and serial port 1..4’s pins when one or more of the units are disabled, allowing the user to utilize them as general-purpose digital I/O pins to communicate to off-chip resources. When controlled by the PPC, peripheral control module (PCM) pins operate similarly to GPIO pins except that they cannot perform edge detection and interrupt generation. The PPC is also used to specify the direction of the peripherals’ pins when sleep mode is entered.

Note that serial ports 1..3 contain individual enables for their transmit and receive serial engines. Thus, if only half-duplex transmission is needed, one pin can be used for serial communication and the other for digital I/O communication. Also note that serial port 0’s pins are dedicated to the USB device controller (UDC), which uses the pins to drive a differential transceiver, preventing them from being used as digital I/O pins when the UDC is disabled.

11.13.1PPC Operation

Following a hardware reset of the SA-1100 (nRESET asserted then negated), all peripheral control module units are disabled, giving control of their pins to the PPC (except serial port 0). The PPC, in turn, configures all peripheral pins it controls as inputs. Once reset is negated, the user should program the peripherals as soon as possible, and configure the pins of any peripheral that is not usable to function as general-purpose I/O signals. This should be done quickly to limit the amount of power consumed at startup because pins that are intended to function as outputs within the system are initially configured as inputs, and the receiving device to which they are connected will float and consume power.

The PPC contains special resources to limit off-chip power consumption during and immediately following the assertion of sleep mode. The PPC contains a sleep mode direction register, which is programmed by the user, and individually configures 22 of the peripherals’ pins either as inputs or outputs during sleep mode. When configured as an output, the pin is forced low in sleep mode. This special register is required because the first action taken when sleep mode is entered is the assertion of reset to all the peripherals, which would, in turn, errantly configure all peripheral pins as inputs. The sleep mode direction register is not reset; the user can maintain the correct direction programmed for each of the peripherals’ pins while in sleep mode. When sleep mode is exited, the user can then reprogram the peripherals and the PPC registers to resume control of the peripherals’ pins. To keep the same pin direction and state after sleep mode has been negated but before the user reprograms the peripherals, the system control module’s power manager maintains the peripherals’ pin direction and state following sleep negation until the peripheral control hold bit (PSSR:PH), located in the power manager, is cleared (by writing a one to it). Therefore, the pin direction and state established during sleep using the sleep mode direction register remains intact following the negation of sleep until the PH bit is cleared. Once PH is cleared, control of the peripherals’ pins is given back to the individual peripherals and to the PPC unit.

Most of the SA-1100’s peripherals can take control of one or more GPIO pins (which are normally controlled within the system control module) to act as input or output triggers, or to drive or supply clocks to the peripherals. The GPIO unit contains a GPIO alternate function register (GAFR) that the user must program to give control of the GPIO pins to the individual peripheral units for each of the alternate functions. The user must also program the GPIO pin direction register (GPDR) for the corresponding pins that are used by the peripheral units. The GPIO pin alternate functions are then enabled within the individual peripherals using a control bit. However, two control bits exist within the PPC that configure six of the GPIO unit’s pins for peripheral alternate functions.

11-184 SA-1100 Developer’s Manual