The LeCroy Model 2378 is a 16-bit Arithmetic Logic Unit (ALU) originally designed at INFN, Rome, Italy, and is now a member of the LeCroy ECLine family of instruments. Use of the LeCroy ECLine standard provides for the advantages of high speed, pipelined architec- ture, and dynamic programming. ECLine high impedance inputs and low impedance outputs permit data transmission via an ECL bus to and from many modules.
The arithmetic operations (addition and subtraction) of the 2378 are expandable to greater than 16 bits by using Carry Out and Carry In signals. Arithmetic operations can be divided into two groups, those that perform an operation on two input words, and those that require only a single input (accumulator mode). Logical operations include bit-by-bit AND, OR, exclusive OR (XOR) and initialization (output = all "1"'s or all "0"'s). All operations are performed within 50 nsec, providing data rates up to 20 MHz.
Operands are presented to the Model 2378 front-panel 34-pin Header inputs A and B. The resultant is given on the Output C which is equipped with a 34-pin Header. Inputs A and B data can be Strobed into the ALU separately or together, and the Output C data ready Strobe is available for strobing the data into the next ECLine module. Connection of these Strobe signals is via 2-pin twisted-pair connectors.
Sixteen different operation codes are available for use. These may be latched in via a multipin header on the front panel for the 4-bit OP- Code, and a Strobe on a 2-pin input. Alternatively, the OP-Code can be set via CAMAC command and retained for all front-panel in- puts. This ability to alter the OP-Code via CAMAC or to perform dynamic OP-Code changes through the front panel provides for a vari- ety of applications in data acquisition systems.
GENERAL
Upon powerup the 2378 is reset to CAMAC access enabled mode. If the front-panel LED is not lit, check power supply voltages, then issue a CAMAC F(26)-A(0) command to enable CAMAC access. The LED should be lit. In this state, the unit may be written with an OP-Code and status lines (FF1, FF2, and FF3) data (see Table 1). This programming is necessary to define the operating mode of the module. If front-panel OP-Code programming is selected, then the OP-Code programmed via CAMAC is overwritten the first time it is written via the front panel. CAMAC readout is accomplished with F(0)-A(0), resulting in a 7-bit readout of the OP-Code and 3 module status lines. A CAMAC F(0)-A(1) gives the 16-bit contents of the C output.
CAMAC COMMANDS
The following CAMAC commands are valid for the LeCroy Model 2378 ALU.
F(0)-A(0) Read latched OP-Code and status lines. The OP-Code appears on CAMAC Read lines R1, R2, R3 and R4 (lower 4 bits), and FF1, FF2, FF3 are on lines R5, R6 and R7 respectively.
F(0)-A(1) Read Output C (16 bits). Data is available on the CAMAC read lines Ri through R16.
F(16)-A(0) Write 4-bit OP-Code and 3-bit status code to ALU. OP-Code is in lowest 4 bits, followed by FF1, FF2, and FF3 in bits 5, 6 and 7.
F(24)-A(0) Disable CAMAC access.
F(25)-A(0) Strobe A and B inputs into latch. Valid only when CAMAC is enabled.
F(26)-A(0) Enables CAMAC access
The status bits FF1, FF2 and FF3 determine the source or destination of some signals internally. If FF1 is set, then the front-panel OP-Code port is active (after CAMAC is disabled). Otherwise, the front-panel OP-Code port is turned off. Signal FF2 determines whether the OP-Code latch is clocked by the front-panel OP-Code Strobe (FF2 set) or by the front-panel Strobe A, either only when CAMAC access is disabled. Signal FF3 is set only to enable a Carry-In for use with >16 bit additions when the module is not the lowest 16 bits. These lines are programmed via a CAMAC F(16)-A(0) command and read with a CAMAC F(0)-A(0) command as indicated above.
FRONT-PANEL STROBES
The data read strobe output on the front panel results from the OR'ing of front-panel Strobes A1, A2, B1 and B2. A pc board jumper sets the delay between Strobe In and data ready output. Strobing the ALU by CAMAC F(25)-A(0) does not produce a data ready output. The OP-Code entered on the front panel (only if bit FF1 is set) is latched either by the OP-Code Strobe input or by the input A Strobe (if bits FF1 and FF2 are set). The OP-Code must be given 20 nsec time prior to an arithmetic or logical operation.
ACCUMULATOR MODE
Some OP-Codes use one input and the previous output as operands. For these operations, input B only is used, and the Output C is multiplexed into the input A register when Strobe B is asserted.
CARRY-IN/CARRY OUT
Arithmetic addition can be extended to more than 16 bits by connecting the Carry Out of one ALU to the Carry In of the next. The Carry In of the ALU is enabled by setting bit FF3, and so must be set in modules that are not handling the lowest 16 bits.