What do you mean by "parameters?" Basically, the program that establishes the STIMERM exit routine must store anything the exit routine requires in storage that is convenient to the exit routine.
The STIMERM macro can specify the address of a 4 byte area that contains some sort of data that may be useful to the exit routine. MVS Assembler Service Reference shows a character string, but it can be an address of something the exit routine can find useful, like an ECB for it to POST to indicate the timer interval has expired. This is much better than the minimal interface provided by the old OS/360 STIMER macro. This is a complete program to wait for 1 second.
WAIT1SEC TITLE ' WAIT FOR ONE SEC>
OND'
SPACE 5
WAIT1SEC CSECT ESTABLISH CSECT
WAIT1SEC AMODE ANY DEFINE THE AMODE
WAIT1SEC RMODE ANY DEFINE THE RMODE
W DSECT DEFINE THE WORK AREA
TPARMS STIMERM SET,MF=L STIMERM PARM LIST
TPARM EQU TPARMS,*-TPARMS DEFINE THE FULL STORAGE AREA FOR ->
STIMERM PARM LIST
PARMWORD DS A PARAMETER PASSED TO THE EXIT ROUTINE
ECB DS F EVENT CONTROL BLOCK POSTED BY THE ->
EXIT ROUTINE
S DS 9D OS/360 SAVE AREA
WL EQU *-W LENGTH OF THE WORK AREA
WAIT1SEC CSECT RETURN TO THE CSECT
USING *,12 ESTABLISH WAIT1SEC ADDRESSABILITY
USING W,11 ESTABLISH WORK AREA ADDRESSABILITY
SAVE (14,12),,WAIT1SEC-&SYSDATE-SYSTIME SAVE REGISTERS
LR 12,15 COPY THE ENTRY POINT ADDRESS TO ->
REG 12
LHI 0,WL LOAD THE LENGTH OF THE WORK AREA
GETMAIN RU,LV=(0),LOC=(ANY,ANY) ALLOCATE THE WORK AREA
LR 11,1 COPY THE WORK AREA ADDRESS TO REG 11
LA 15,S LOAD THE ADDR OF THE NEW SAVE AREA
ST 13,4(,15) ADD THE NEW SAVE AREA
ST 15,8(,13) TO THE SAVE AREA CHAIN
LR 13,15 ESTABLISH THE NEW SAVE AREA POINTER
MVI ECB,0 SET THE ECB AS NOT WAITING, ->
NOT POSTED
ST 11,PARMWORD STORE THE WORK AREA ADDRESS IN ->
PARMWORD
MVC TPARM,TPARMM COPY THE MASTER STIMERM PARM LIST ->
TO THE WORK AREA
STIMERM SET,BINTVL==F'100',WAIT=NO,EXIT=ITIMEUP, ESTABLISH ->
ID=TIMEID,PARM=PARMWORD,MF=(E,TPARM) A TIMER INTERVAL
WAITMAC WAIT 1,ECB=ECB WAIT FOR THE TIMER INTERVAL TO ->
COMPLETE
L 13,4(,13) LOAD THE ADDRESS OF THE PREVIOUS ->
SAVE AREA
LHI 0,WL LOAD THE LENGTH OF THE WORK AREA
FREEMAIN RU,A=(11),LV=(0) FREE THE WORK AREA
RETURN (14,12),T,RC=0 RESTORE REGS & RETURN
DC 0D'0' FORCE DOUBLE WORD ALIGNMENT
USING *,12 ESTABLISH STIMERM EXIT ROUTINE ->
ADDRESSABILITY (WORK AREA ->
ADDRESSABILITY IS INHERITED ->
BECAUSE IT WAS NEVER DROPPED)
ITIMEUP SAVE (14,12),,ITIMEUP SAVE REGISTERS IN THE SAVE AREA ->
AREA PROVIDED BY THE TIMER ->
INTERRUPT ROUTINE
LR 12,15 COPY THE ADDRESS OF ITIMEUP TO ->
REG 12
L 11,4(,1) LOAD THE ADDRES OF THE WAIT1SEC ->
WORK AREA
POST ECB,0 POST THE COMPLETTION ECB
RETURN (14,12) RESTORE REGISTERS & RETURN TO THE ->
MVS TIMER INTERRUPT FUNCTION
TPARMM STIMERM SET,MF=L MASTER STIMERM PARM LIST
TIMEID DC CL4'TIME' TIMER ID
DC 0D'0' FORCE DOUBLE WORD ALIGNMENT
LTORG , DEFINE THE WAIT1SEC LITERAL POOL
END WAIT1SEC