
ADSP-21261
Rev. 0
|
Page 11  of 44
|
March 2006
PIN FUNCTION DESCRIPTIONS
ADSP-21261 pin definitions are listed below. Inputs identified 
as synchronous (S) must meet timing requirements with respect 
to CLKIN (or with respect to TCK for TMS, TDI). Inputs iden-
tified as asynchronous (A) can be asserted asynchronously to 
CLKIN (or to TCK for TRST). Tie or pull unused inputs to 
V
DDEXT
 or GND, except for the following:
 DAI_Px, SPICLK, MISO, MOSI, EMU, TMS,TRST, TDI, 
and AD15–0 (NOTE: These pins have internal pull-up 
resistors.)
The following symbols appear in the Type column of 
Table 2
: 
A = asynchronous, G = ground, I = input, O = output, 
P = power supply, S = synchronous, (A/D) = active drive, 
(O/D) = open drain, and T = three-state. 
Table 2. Pin Function Descriptions
Pin 
AD15–0
Type
I/O/T
State During and 
After Reset
AD15–0 pins are 
driven low both 
during and after 
reset
Function
Parallel Port Address/Data.
 The ADSP-21261 parallel port and its corresponding 
DMA unit output addresses and data for peripherals on these multiplexed pins. The 
multiplex state is determined by the ALE pin. The parallel port can operate in either 
8-bit or 16-bit mode. Each AD pin has a 22.5 k
Ω
 internal pull-up resistor. See 
Address 
Data Modes on Page 14
 for details of the AD pin operation.
For 8-bit mode: ALE is automatically asserted whenever a change occurs in the 
upper 16 external address bits, A23–8; ALE is used in conjunction with an external 
latch to retain the values of the A23–8.
For 16-bit mode: ALE is automatically asserted whenever a change occurs in the 
address bits, A15–0; ALE is used in conjunction with an external latch to retain the 
values of the A15–0. To use these pins as flags (FLAG15–0) set (=1) Bit 20 of the 
SYSCTL register and disable the parallel port. See 
Table 3 on Page 14
 for a list of how 
the AD15–0 pins map to the flag pins. When configured in the IDP_PDAP_CTL 
register, the IDP Channel 0 can use these pins for parallel input data.
Parallel Port Read Enable.
 RD is asserted low whenever the DSP reads 8-bit or 
16-bit data from an external memory device. When AD15–0 are flags, this pin 
remains deasserted.
Parallel Port Write Enable.
 WR is asserted low whenever the DSP writes 8-bit or 
16-bit data to an external memory device. When AD15–0 are flags, this pin remains 
deasserted.
Parallel Port Address Latch Enable.
 ALE is asserted whenever the DSP drives a 
new address on the parallel port address pin. On reset, ALE is active high. However, 
it can be reconfigured using software to be active low. When AD15–0 are flags, this 
pin remains deasserted.
Flag Pins.
 Each FLAG pin is configured via control bits as either an input or output. 
As an input, it can be tested as a condition. As an output, it can be used to signal 
external peripherals. These pins can be used as an SPI slave select output during SPI 
mastering. These pins are also multiplexed with the IRQx and the TIMEXP signals.
In SPI master boot mode, FLAG0 is the slave select pin that must be connected to 
an SPI EPROM. FLAG0 is configured as a slave select during SPI master boot. When 
Bit 16 is set (=1) in the SYSCTL register, FLAG0 is configured as IRQ0.
When Bit 17 is set (=1) in the SYSCTL register, FLAG1 is configured as IRQ1.
When Bit 18 is set (=1) in the SYSCTL register, FLAG2 is configured as IRQ2.
When Bit 19 is set (=1) in the SYSCTL register, FLAG3 is configured as TIMEXP, which 
indicates that the system timer has expired.
RD
O
Output only, driven 
high
1
WR
O
Output only, driven 
high
1
ALE
O
Output only, driven 
low
1
FLAG3–0
I/O/A
Three-state