Motorola ColdFire MCF5281 - Manual (Page 543)

Queued Analog-to-Digital Converter (QADC)
Freescale Semiconductor 28-5
28.4.2.2 Port QB Digital I/O Signals
Port QB signals are referred to as PQB[3:0] when used as a 4-bit digital input/output port. In addition to
functioning as analog input signals, the port QB signals are also connected to the input of a synchronizer
during reads and may be used as general-purpose digital inputs when the applied voltages meet V
IH
and
V
IL
requirements.
Each port QB signal is configured as an input or output by programming the port data direction register
(DDRQB). The digital input signal states are read from the port QB data register (PORTQB) when
DDRQB specifies that the signals are inputs. The digital data in PORTQB is driven onto the port QB
signals when the corresponding bits in DDRQB specify output. See
Section 28.6.4, “Port QA and QB Data
Direction Register (DDRQA & DDRQB) .
28.4.3 External Trigger Input Signals
The QADC has two external trigger signals, ETRIG2 and ETRIG1. Each external trigger input is
associated with one of the scan queues, queue 1 or queue 2. The assignment of ETRIG[2:1] to a queue is
made by the TRG bit in QADC control register 0 (QACR0). When TRG = 0, ETRIG1 triggers queue 1 and
ETRIG2 triggers queue 2. When TRG = 1, ETRIG1 triggers queue 2 and ETRIG2 triggers queue 1. See
Section 28.6.5, “Control Registers “Control Registers.”
28.4.4 Multiplexed Address Output Signals
In non-multiplexed mode, the QADC analog input signals are connected to an internal multiplexer which
routes the analog signals into the internal A/D converter.
In externally multiplexed mode, the QADC allows automatic channel selection through up to four external
4-to-1 multiplexer chips. The QADC provides a 2-bit multiplexed address output to the external
multiplexer chips to allow selection of one of four inputs. The multiplexed address output signals, MA1
and MA0, can be used as multiplexed address output bits or as general-purpose I/O when external
multiplexed mode is not being used.
MA[1:0] are used as the address inputs for up to four 4-channel multiplexer chips. Because the MA[1:0]
signals are digital outputs in multiplexed mode, the state of their corresponding data direction bits in
DDRQA is ignored.
28.4.5 Multiplexed Analog Input Signals
In external multiplexed mode, four of the port QB signals are redefined so that each represent four analog
input channels. See
Table 28-1 .
Table 28-1. Multiplexed Analog Input Channels
Multiplexed
Analog Input
Channels
ANW Even numbered channels from 0 to 6
ANX Odd numbered channels from 1 to 7
ANY Even numbered channels from 16 to 22
ANZ Odd numbered channels from 17 to 23
MCF5282 and MCF5216 ColdFire Microcontroller User’s Manual, Rev. 3