ICL7109CPL datasheet(14/25 Pages) INTERSIL

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Handshake Mode

The handshake output mode is provided as an alternative

means of interfacing the ICL7109 to digital systems where the

A/D converter becomes active in controlling the flow of data

instead of passively responding to chip and byte enable

inputs. This mode is specifically designed to allow a direct

interface between the ICL7109 and industry-standard UARTs

(such as the Intersil IM6402/3) with no external logic required.

When triggered into the handshake mode, the ICL7109 pro-

vides all the control and flag signals necessary to sequentially

transfer two bytes of data into the UART and initiate their

transmission in serial form. This greatly eases the task and

reduces the cost of designing remote data acquisition stations

using serial data transmission.

Entry into the handshake mode is controlled by the MODE pin.

When the MODE terminal is held high, the ICL7109 will enter

the handshake mode after new data has been stored in the out-

put latches at the end of a conversion (See Figures 7 and 8).

The MODE terminal may also be used to trigger entry into the

handshake mode on demand. At any time during the conver-

sion cycle, the low to high transition of a short pulse at the

MODE input will cause immediate entry into the handshake

mode. If this pulse occurs while new data is being stored, the

entry into handshake mode is delayed until the data is stable.

While the converter is in the handshake mode, the MODE input

is ignored, and although conversions will still be performed,

data updating will be inhibited (See Figure 9) until the converter

completes the output cycle and clears the handshake mode.

When the converter enters the handshake mode, or when the

MODE input is high, the chip and byte enable terminals

become TTL-compatible outputs which provide the control

signals for the output cycle (See Figures 7, 8, and 9).

In handshake mode, the SEND input is used by the converter

as an indication of the ability of the receiving device (such as a

UART) to accept data.

Figure 7 shows the sequence of the output cycle with SEND

held high. The handshake mode (Internal MODE high) is

entered after the data latch pulse, and since MODE remains

high the CE/LOAD, LBEN and HBEN terminals are active as

outputs. The high level at the SEND input is sensed on the

same high to low internal clock edge that terminates the data

latch pulse. On the next low to high internal clock edge the

CE/LOAD and the HBEN outputs assume a low level, and the

high-order byte (Bits 9 through 12, POL, and OR) outputs are

enabled. The CE/LOAD output remains low for one full internal

clock period only, the data outputs remain active for 11/2 inter-

nal clock periods, and the high byte enable remains low for two

clock periods. Thus the CE/LOAD output low level or low to

high edge may be used as a synchronizing signal to ensure

valid data, and the byte enable as an output may be used as a

byte identification flag. With SEND remaining high the converter

completes the output cycle using CE/LOAD and LBEN while

the low order byte outputs (bits 1 through 8) are activated. The

handshake mode is terminated when both bytes are sent.

Figure 8 shows an output sequence where the SEND input is

used to delay portions of the sequence, or handshake to ensure

correct data transfer. This timing diagram shows the relation-

ships that occur using an industry-standard IM6402/3 CMOS

UART to interface to serial data channels. In this interface, the

SEND input to the ICL7109 is driven by the TBRE (Transmitter

Buffer Register Empty) output of the UART, and the CE/LOAD

terminal of the ICL7109 drives the TBRL (Transmitter Buffer

leled into the eight Transmitter Buffer Register inputs.

FIGURE 6. DIRECT MODE OUTPUT TIMING

TABLE 1. DIRECT MODE TIMING REQUIREMENTS

(See Note 4 of Electrical Specifications)

DESCRIPTION

SYMBOL

MIN

TYP

MAX

UNITS

DATA

VALID

DATA

VALID

DATA

VALID

tCEA

tBEA

tDAB

tDHB

tDAC

tDHC

CE/LOAD

AS INPUT

HBEN

AS INPUT

LBEN

AS INPUT

HIGH BYTE

DATA

LOW BYTE

DATA

= HIGH IMPEDANCE

ICL7109

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