SERIAL INTERFACE ADAPTER FOR
TC500 A/D CONVERTER FAMILY
TC520A
PIN DESCRIPTIONS (Cont.)
Pin No.
Pin No.
14-Pin PDIP 16-Pin SOIC
Package
Package
Symbol
Description
11
13
DIN
Input, logic level. Serial port input pin. The TC5xx A/D converter integration
time (TINT) and Autozero time (TAZ) values are determined by the LOAD
VALUE byte clocked into this pin. This initialization must take place at power
up, and can be rewritten (or modified and rewritten) at any time. The LOAD
VALUE is clocked into DIN MSB first.
12
14
LOAD
Input, active low; level and edge triggered. The LOAD VALUE is clocked into
the 8 bit shift register on board the TC520A while LOAD is held low. The LOAD
VALUE is then transferred into the TC520A internal timebase counter (and
becomes effective) when LOAD is returned high. If so desired, LOAD can be
momentarily pulsed low (eliminating the need to clock a LOAD VALUE into
DIN). In this case, the current state of DIN is clocked into the TC520A timebase
counter selecting either a count of 65536 (DIN = High), or count of 32768 (DIN = Low).
13
14
15
16
DV
CE
Output, active low. DV is brought any time the TC520A is in the AZ phase of
conversion. This occurs when either the TC520A initiates a normal AZ phase
by setting A, B, equal to 01; or when CE is pulled high (which overrides the
normal A, B sequencing and forces an AZ state). DV is returned high when the
TC520A exits AZ.
Input, active low, level triggered. Conversion will be continuously performed as
long as CE remains low. Pulling CE high causes the conversion process to be
halted, and forces the TC520 into the AZ mode for as long as CE remains
high. CE should be taken high whenever it is necessary to momentarily
suspend conversion (for example: to change the address lines of an input
multiplexer). CE should be pulled high only when the TC520A enters an AZ
phase (i.e. when DV is low). This is necessary to avoid excessively long
integrator discharge times which could result in erroneous conversion. This pin
should be grounded if unused. It should be left floating if a 0.01µF RESET
capacitor is connected to it (see Applications section).
DETAILED DESCRIPTION (CONT.)
TC520A Timing
A, B have been sequenced through the required 4 phases of
conversion: Auto Zero (AZ), Integrate (INT), De-integrate
(DINT)andIntegratorZero(IZ)(SeeFigure1). TheAutoZero
phase compensates for offset errors in the TC5xx A/D
converter. The integrate phase connects the voltage to be
converted to the TC5xx A/D converter input (resulting in an
integrator output dv/dt directly proportional to the magnitude
of the applied input voltage). Actual A/D conversion (count-
ing) is initiated at the start of the DINT phase and terminates
when the integrator output crosses 0V. The integrator output
is then forced to 0V during the IZ phase and the converter is
ready for another cycle. Please see the TC500/500A/510/
514 data sheet for a complete description of these phases.
The number of SYSCLK periods (counts) for the AZ and
INT phases is determined by the LOAD VALUE. The LOAD
VALUE is a single byte that must be loaded into the most
significantbyteof16bitcounteron-boardtheTC520Aduring
initialization. The lower byte of this counter is pre-loaded to
a value of 0FFH (25610) and cannot be changed.
TheTC520Aconsistsofaserialportandstatemachine.
ThestatemachineprovidescontroltimingtoboththeTC5xx
A/DconverterconnectedtotheTC520A, aswellassequen-
tial timing for TC520A internal operation. All timing is de-
rivedfromthefrequencysourceatOSCIN andOSCout.This
frequencysourcecanbeeitheranexternally-providedclock
signal,orexternalcrystal.Ifanexternalclockisused,itmust
be connected to the OSCIN pin and OSCOUT must remain
floating.
If a crystal is used, it must be connected between the
OSCIN and OSCOUT and physically located as close to the
OSCIN and OSCOUT pins as possible. The incoming fre-
quency is internally divided by 4 and the resulting clock
(SYSCLK) controls all timing functions.
TC5xx A/D Converter Control Signals
The TC520A control outputs (A, B) and control input
(CMPTR) connect directly to the corresponding pins of the
TC5xx A/D converter. A conversion is consummated when
The LOAD VALUE (upper 8 bits of the counter) can be
programmed over a range of 0FFH to 00H (corresponding to
3-42
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