Intel STRONGARM SA-1100 - Manual (Page 340)

11-190 SA-1100 Developer’s Manual
Peripheral Control Module
11.13.6 PPC Sleep Mode Pin Direction Register
When sleep mode is entered, reset is asserted to all of the SA-1100’s peripherals and to the PPC unit.
The PPC pin direction register is cleared during a hard, soft, or sleep reset, causing the peripheral pins
under the PPC’s control to be configured as inputs. If this register were also used to determine pin
direction during sleep, the pins would all be configured as inputs. This action would cause any off-chip
device that expects data to be output from the SA-1100 to burn power during sleep because its input
would float. The sleep mode pin direction register (PSDR) prevents this undesired power consumption
by allowing the user to establish peripheral pin direction during and immediately following sleep mode.
When sleep mode is entered, both the peripherals and the PPC are reset; however, PSDR is not reset
like PPDR. Once the user programs PSDR, it retains its data after sleep mode is entered and reset is
asserted. The power manager uses the values in PSDR to determine the direction and state of the 22
peripheral pins. When a sleep mode direction bit is programmed to a zero, the corresponding pin is
configured as an output and is driven low (zero). If it is programmed to a one, it is an input. The
power manager latches the contents of PSDR before VDD is removed from the SA-1100 to maintain
the peripheral pin direction and state after the main power supply is removed. Once VDD is removed,
the data in PSDR is lost and must be reprogrammed after exiting sleep mode. The power manager
contains a control bit called the peripheral control hold (PSSR:PH). This bit is set upon exit from
sleep mode and indicates that the peripheral pins are being held in their sleep state. Following sleep,
the user should first reprogram the peripherals and the PPC, then clear PH (by writing a one to it) in
order to give control of the pins back to the peripheral units. Note that sleep mode invocation causes
RPP to be cleared so that the pins are once again held in their sleep state until the user can set RPP.
See
Chapter 9, “System Control Module” .
Because the peripherals are reset when sleep mode is entered, serial port 2’s transmit and receive
pin (TXD2 and RXD2) polarity bits (TXP and RXP) are both reset to one, which configures
transmit and receive data as true or noninverted data. Thus the user need not reprogram these bits
prior to the invocation of sleep mode.
Note that PPSR is initialized only by a hardware or power-on reset (negation of the nRESET pin). It is
not affected by a software reset or a reset that occurs as a result of the SA-1100 entering sleep mode.
Also note that for reserved bits, writes are ignored and reads return zero. The following table shows
the location of each sleep mode pin direction bit and to which peripheral pin it corresponds.
Address: 0h 9006 000C PSDR: PPC Sleep Mode Pin Direction Register Read/Write
Bit 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16
Reserved SFRM SCLK RXD4 TXD4 RXD3 TXD3
Hard Reset 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1
Bit 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
RXD
2
TXD2 RXD1 TXD1
L_
BIAS
L_
FCLK
L_
LCLK
L_
PCLK
LDD
<7>
LDD
<6>
LDD
<5>
LDD
<4>
LDD
<3>
LDD
<2>
LDD
<1>
LDD
<0>
Hard Reset 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1