MC94MX21 Technical Data, Rev. 1.
5
6
Freescale Semiconductor
Signal Descriptions
SDRAM Controller
SDBA [4:0]
SDRAM non-interleave mode bank address signals. These signals are multiplexed with address signals
A[20:16].
SDIBA [3:0]
SDRAM interleave addressing mode bank address signals. These signals are multiplexed with address
signals A[24:21].
MA [11:0]
SDRAM address signals. MA[9:0] are multiplexed with address signals A[10:1].
DQM [3:0]
SDRAM data qualifier mask multiplexed with EB[3:0]. DQM3 corresponds to D[31:24], DQM2
corresponds to D[23:16], DQM1 corresponds to D[15:8], and DQM0 corresponds to D[7:0].
CSD0
SDRAM Chip Select signal. This signal is multiplexed with the CS2 signal. This signal is selectable by
programming the Function Multiplexing Control Register in the System Control chapter.
CSD1
SDRAM Chip Select signal. This signal is multiplexed with the CS3 signal. This signal is selectable by
programming the Function Multiplexing Control Register in the System Control chapter.
RAS
SDRAM Row Address Select signal.
CAS
SDRAM Column Address Select signal
SDWE
SDRAM Write Enable signal
SDCKE0
SDRAM Clock Enable 0
SDCKE1
SDRAM Clock Enable 1
SDCLK
SDRAM Clock
Clocks and Resets
EXTAL26M
Crystal input (26MHz), or a 16 MHz to 32 MHz oscillator (or square-wave) input when the internal
oscillator circuit is shut down. When using an external signal source, feed this input with a square wave
signal switching from GND to VDDA.
XTAL26M
Oscillator output to external crystal. When using an external signal source, float this output.
EXTAL32K
32 kHz or 32.768 kHz crystal input. When using an external signal source, feed this input with a square
wave signal switching from GND to QVDD5.
XTAL32K
Oscillator output to external crystal. When using an external signal source, float this output.
CLKO
Clock Out signal selected from internal clock signals. Please refer to clock controller for internal clock
selection.
EXT_48M
This is a special factory test signal. To ensure proper operation, connect this signal to ground.
EXT_266M
This is a special factory test signal. To ensure proper operation, connect this signal to ground.
RESET_IN
Master Reset—External active low Schmitt trigger input signal. When this signal goes active, all modules
(except the reset module, SDRAMC module, and the clock control module) are reset.
RESET_OUT
Reset Out—Internal active low output signal from the Watchdog Timer module and is asserted from the
following sources: Power-on reset, External reset (RESET_IN), and Watchdog time-out.
POR
Power On Reset—Active low Schmitt trigger input signal. The POR signal is normally generated by an
external RC circuit designed to detect a power-up event.
CLKMODE[1:0]
These are special factory test signals. To ensure proper operation, leave these signals as no connects.
OSC26M_TEST
This is a special factory test signal. To ensure proper operation, leave this signal as a no connect.
TEST_WB[2:0]
These are special factory test signals. However, these signals are also multiplexed with GPIO PORT E
as well as alternate keypad signals. If not using these signals for GPIO functions or for other multiplexed
functions, then configure as GPIO input with pull-up enabled, and leave as a no connect.
Table 2. i.MX21 Signal Descriptions (Continued)
Signal Name
Function/Notes
Because
of
an
order
from
the
United
States
International
Trade
Commission,
BGA-packaged
product
lines
and
part
numbers
indicated
here
currently
are
not
available
from
Freescale
for
import
or
sale
in
the
United
States
prior
to
September
2010:
MC94MX21DVKN3